Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $134.36   13.860%   $152.9823   $152.98   $153.00   $153.00  
  Purchase #2 $119.60   5.621%   $126.3227   $126.32   $126.30   $126.30  
  Purchase #3 $126.37   9.644%   $138.5571   $138.56   $138.55   $138.60  
  Purchase #4 $195.82   5.570%   $206.7272   $206.73   $206.75   $206.70  
  Purchase #5 $233.55   12.123%   $261.8633   $261.86   $261.85   $261.90  
  Purchase #6 $101.42   3.126%   $104.5904   $104.59   $104.60   $104.60  
  Purchase #7 $242.25   5.562%   $255.7239   $255.72   $255.70   $255.70  
  7 purchase totals = $1,153.37       $1,246.7669   $1,246.76   $1,246.75   $1,246.80