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 $229.60   7.540%   $246.9118   $246.91   $246.90   $246.90  
  Purchase #2 $228.88   11.551%   $255.3179   $255.32   $255.30   $255.30  
  Purchase #3 $237.81   10.618%   $263.0607   $263.06   $263.05   $263.10  
  Purchase #4 $16.92   3.714%   $17.5484   $17.55   $17.55   $17.50  
  Purchase #5 $16.85   10.381%   $18.5992   $18.60   $18.60   $18.60  
  Purchase #6 $140.90   6.852%   $150.5545   $150.55   $150.55   $150.60  
  Purchase #7 $21.41   3.597%   $22.1801   $22.18   $22.20   $22.20  
  7 purchase totals = $892.37       $974.1726   $974.17   $974.15   $974.20