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 $183.48   11.386%   $204.371   $204.37   $204.35   $204.40  
  Purchase #2 $35.85   10.357%   $39.563   $39.56   $39.55   $39.60  
  Purchase #3 $14.61   5.765%   $15.4523   $15.45   $15.45   $15.50  
  Purchase #4 $49.91   5.351%   $52.5807   $52.58   $52.60   $52.60  
  Purchase #5 $154.89   9.343%   $169.3614   $169.36   $169.35   $169.40  
  Purchase #6 $78.49   7.212%   $84.1507   $84.15   $84.15   $84.20  
  Purchase #7 $173.71   6.345%   $184.7319   $184.73   $184.75   $184.70  
  7 purchase totals = $690.94       $750.2110   $750.20   $750.20   $750.40