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 $216.84   11.146%   $241.009   $241.01   $241.00   $241.00  
  Purchase #2 $87.85   13.601%   $99.7985   $99.80   $99.80   $99.80  
  Purchase #3 $55.79   8.662%   $60.6225   $60.62   $60.60   $60.60  
  Purchase #4 $73.86   4.214%   $76.9725   $76.97   $76.95   $77.00  
  Purchase #5 $200.32   13.290%   $226.9425   $226.94   $226.95   $226.90  
  Purchase #6 $151.91   11.838%   $169.8931   $169.89   $169.90   $169.90  
  Purchase #7 $68.29   10.868%   $75.7118   $75.71   $75.70   $75.70  
  7 purchase totals = $854.86       $950.9499   $950.94   $950.90   $950.90