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 $82.27   12.531%   $92.5793   $92.58   $92.60   $92.60  
  Purchase #2 $190.41   4.600%   $199.1689   $199.17   $199.15   $199.20  
  Purchase #3 $45.27   10.102%   $49.8432   $49.84   $49.85   $49.80  
  Purchase #4 $13.95   9.114%   $15.2214   $15.22   $15.20   $15.20  
  Purchase #5 $209.45   6.129%   $222.2872   $222.29   $222.30   $222.30  
  Purchase #6 $68.74   6.452%   $73.1751   $73.18   $73.20   $73.20  
  Purchase #7 $187.43   9.118%   $204.5199   $204.52   $204.50   $204.50  
  7 purchase totals = $797.52       $856.7950   $856.80   $856.80   $856.80