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 $69.83   9.171%   $76.2341   $76.23   $76.25   $76.20  
  Purchase #2 $162.55   6.764%   $173.5449   $173.54   $173.55   $173.50  
  Purchase #3 $54.97   10.358%   $60.6638   $60.66   $60.65   $60.70  
  Purchase #4 $197.75   3.845%   $205.3535   $205.35   $205.35   $205.40  
  Purchase #5 $115.59   5.660%   $122.1324   $122.13   $122.15   $122.10  
  Purchase #6 $77.32   9.743%   $84.8533   $84.85   $84.85   $84.90  
  Purchase #7 $244.86   3.448%   $253.3028   $253.30   $253.30   $253.30  
  7 purchase totals = $922.87       $976.0848   $976.06   $976.10   $976.10