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 $163.76   3.531%   $169.5424   $169.54   $169.55   $169.50  
  Purchase #2 $94.55   8.197%   $102.3003   $102.30   $102.30   $102.30  
  Purchase #3 $47.57   11.439%   $53.0115   $53.01   $53.00   $53.00  
  Purchase #4 $106.53   12.358%   $119.695   $119.70   $119.70   $119.70  
  Purchase #5 $107.94   7.754%   $116.3097   $116.31   $116.30   $116.30  
  Purchase #6 $244.82   12.511%   $275.4494   $275.45   $275.45   $275.40  
  Purchase #7 $134.28   11.159%   $149.2643   $149.26   $149.25   $149.30  
  7 purchase totals = $899.45       $985.5726   $985.57   $985.55   $985.50