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 $64.65   5.726%   $68.3519   $68.35   $68.35   $68.40  
  Purchase #2 $96.83   3.525%   $100.2433   $100.24   $100.25   $100.20  
  Purchase #3 $201.64   12.151%   $226.1413   $226.14   $226.15   $226.10  
  Purchase #4 $63.38   11.756%   $70.831   $70.83   $70.85   $70.80  
  Purchase #5 $247.89   8.533%   $269.0425   $269.04   $269.05   $269.00  
  Purchase #6 $102.67   5.659%   $108.4801   $108.48   $108.50   $108.50  
  Purchase #7 $49.51   3.525%   $51.2552   $51.26   $51.25   $51.30  
  7 purchase totals = $826.57       $894.3453   $894.34   $894.40   $894.30