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 $62.81   7.828%   $67.7268   $67.73   $67.75   $67.70  
  Purchase #2 $221.85   8.539%   $240.7938   $240.79   $240.80   $240.80  
  Purchase #3 $149.74   13.455%   $169.8875   $169.89   $169.90   $169.90  
  Purchase #4 $60.66   3.782%   $62.9542   $62.95   $62.95   $63.00  
  Purchase #5 $205.80   5.643%   $217.4133   $217.41   $217.40   $217.40  
  Purchase #6 $11.54   9.115%   $12.5919   $12.59   $12.60   $12.60  
  Purchase #7 $91.66   8.302%   $99.2696   $99.27   $99.25   $99.30  
  7 purchase totals = $804.06       $870.6371   $870.63   $870.65   $870.70