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 $61.40   7.604%   $66.0689   $66.07   $66.05   $66.10  
  Purchase #2 $193.62   8.164%   $209.4271   $209.43   $209.45   $209.40  
  Purchase #3 $35.76   9.514%   $39.1622   $39.16   $39.15   $39.20  
  Purchase #4 $210.87   3.526%   $218.3053   $218.31   $218.30   $218.30  
  Purchase #5 $250.30   8.622%   $271.8809   $271.88   $271.90   $271.90  
  Purchase #6 $224.39   3.219%   $231.6131   $231.61   $231.60   $231.60  
  Purchase #7 $11.76   7.673%   $12.6623   $12.66   $12.65   $12.70  
  7 purchase totals = $988.10       $1,049.1198   $1,049.12   $1,049.10   $1,049.20