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 $191.82   6.843%   $204.9462   $204.95   $204.95   $204.90  
  Purchase #2 $62.66   7.261%   $67.2097   $67.21   $67.20   $67.20  
  Purchase #3 $242.65   9.208%   $264.9932   $264.99   $265.00   $265.00  
  Purchase #4 $59.88   6.436%   $63.7339   $63.73   $63.75   $63.70  
  Purchase #5 $10.81   4.761%   $11.3247   $11.32   $11.30   $11.30  
  Purchase #6 $76.29   12.862%   $86.1024   $86.10   $86.10   $86.10  
  Purchase #7 $78.38   6.535%   $83.5021   $83.50   $83.50   $83.50  
  7 purchase totals = $722.49       $781.8122   $781.80   $781.80   $781.70