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 $58.78   8.569%   $63.8169   $63.82   $63.80   $63.80  
  Purchase #2 $61.86   10.766%   $68.5198   $68.52   $68.50   $68.50  
  Purchase #3 $140.95   8.798%   $153.3508   $153.35   $153.35   $153.40  
  Purchase #4 $85.73   11.595%   $95.6704   $95.67   $95.65   $95.70  
  Purchase #5 $21.60   10.790%   $23.9306   $23.93   $23.95   $23.90  
  Purchase #6 $112.31   13.656%   $127.6471   $127.65   $127.65   $127.60  
  Purchase #7 $217.70   5.652%   $230.0044   $230.00   $230.00   $230.00  
  7 purchase totals = $698.93       $762.9400   $762.94   $762.90   $762.90