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 $55.57   9.340%   $60.7602   $60.76   $60.75   $60.80  
  Purchase #2 $229.80   10.570%   $254.0899   $254.09   $254.10   $254.10  
  Purchase #3 $13.65   10.676%   $15.1073   $15.11   $15.10   $15.10  
  Purchase #4 $126.71   13.763%   $144.1491   $144.15   $144.15   $144.10  
  Purchase #5 $111.54   11.698%   $124.5879   $124.59   $124.60   $124.60  
  Purchase #6 $208.30   8.341%   $225.6743   $225.67   $225.65   $225.70  
  Purchase #7 $129.57   10.763%   $143.5156   $143.52   $143.50   $143.50  
  7 purchase totals = $875.14       $967.8843   $967.89   $967.85   $967.90