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 $101.47   10.426%   $112.0493   $112.05   $112.05   $112.00  
  Purchase #2 $185.88   9.658%   $203.8323   $203.83   $203.85   $203.80  
  Purchase #3 $113.61   4.763%   $119.0212   $119.02   $119.00   $119.00  
  Purchase #4 $66.25   10.731%   $73.3593   $73.36   $73.35   $73.40  
  Purchase #5 $101.71   4.568%   $106.3561   $106.36   $106.35   $106.40  
  Purchase #6 $173.52   6.192%   $184.2644   $184.26   $184.25   $184.30  
  Purchase #7 $137.92   7.575%   $148.3674   $148.37   $148.35   $148.40  
  7 purchase totals = $880.36       $947.2500   $947.25   $947.20   $947.30