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 $205.58   3.595%   $212.9706   $212.97   $212.95   $213.00  
  Purchase #2 $235.72   4.243%   $245.7216   $245.72   $245.70   $245.70  
  Purchase #3 $49.73   7.232%   $53.3265   $53.33   $53.35   $53.30  
  Purchase #4 $134.27   13.113%   $151.8768   $151.88   $151.90   $151.90  
  Purchase #5 $135.90   9.781%   $149.1924   $149.19   $149.20   $149.20  
  Purchase #6 $58.58   12.638%   $65.9833   $65.98   $66.00   $66.00  
  Purchase #7 $69.83   8.720%   $75.9192   $75.92   $75.90   $75.90  
  7 purchase totals = $889.61       $954.9904   $954.99   $955.00   $955.00