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 $92.54   12.286%   $103.9095   $103.91   $103.90   $103.90  
  Purchase #2 $28.78   11.248%   $32.0172   $32.02   $32.00   $32.00  
  Purchase #3 $29.88   12.809%   $33.7073   $33.71   $33.70   $33.70  
  Purchase #4 $216.62   3.678%   $224.5873   $224.59   $224.60   $224.60  
  Purchase #5 $44.32   6.643%   $47.2642   $47.26   $47.25   $47.30  
  Purchase #6 $238.90   3.477%   $247.2066   $247.21   $247.20   $247.20  
  Purchase #7 $68.56   12.131%   $76.877   $76.88   $76.90   $76.90  
  7 purchase totals = $719.60       $765.5691   $765.58   $765.55   $765.60