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 $66.49   12.740%   $74.9608   $74.96   $74.95   $75.00  
  Purchase #2 $229.33   9.627%   $251.4076   $251.41   $251.40   $251.40  
  Purchase #3 $247.33   11.214%   $275.0656   $275.07   $275.05   $275.10  
  Purchase #4 $158.92   10.299%   $175.2872   $175.29   $175.30   $175.30  
  Purchase #5 $169.62   9.609%   $185.9188   $185.92   $185.90   $185.90  
  Purchase #6 $172.90   5.725%   $182.7985   $182.80   $182.80   $182.80  
  Purchase #7 $224.50   13.467%   $254.7334   $254.73   $254.75   $254.70  
  7 purchase totals = $1,269.09       $1,400.1719   $1,400.18   $1,400.15   $1,400.20