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 $91.81   10.563%   $101.5079   $101.51   $101.50   $101.50  
  Purchase #2 $45.51   12.173%   $51.0499   $51.05   $51.05   $51.00  
  Purchase #3 $125.42   10.714%   $138.8575   $138.86   $138.85   $138.90  
  Purchase #4 $78.56   9.140%   $85.7404   $85.74   $85.75   $85.70  
  Purchase #5 $60.35   11.610%   $67.3566   $67.36   $67.35   $67.40  
  Purchase #6 $154.96   5.378%   $163.2937   $163.29   $163.30   $163.30  
  Purchase #7 $178.72   12.190%   $200.506   $200.51   $200.50   $200.50  
  7 purchase totals = $735.33       $808.3120   $808.32   $808.30   $808.30