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 $149.96   13.519%   $170.2331   $170.23   $170.25   $170.20  
  Purchase #2 $147.96   4.303%   $154.3267   $154.33   $154.35   $154.30  
  Purchase #3 $97.80   4.227%   $101.934   $101.93   $101.95   $101.90  
  Purchase #4 $216.30   9.689%   $237.2573   $237.26   $237.25   $237.30  
  Purchase #5 $48.58   6.234%   $51.6085   $51.61   $51.60   $51.60  
  Purchase #6 $106.30   12.193%   $119.2612   $119.26   $119.25   $119.30  
  Purchase #7 $181.79   11.785%   $203.214   $203.21   $203.20   $203.20  
  7 purchase totals = $948.69       $1,037.8348   $1,037.83   $1,037.85   $1,037.80