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 $89.42   7.288%   $95.9369   $95.94   $95.95   $95.90  
  Purchase #2 $54.93   5.567%   $57.988   $57.99   $58.00   $58.00  
  Purchase #3 $19.33   12.424%   $21.7316   $21.73   $21.75   $21.70  
  Purchase #4 $105.66   9.276%   $115.461   $115.46   $115.45   $115.50  
  Purchase #5 $119.65   9.528%   $131.0503   $131.05   $131.05   $131.10  
  Purchase #6 $170.95   5.857%   $180.9625   $180.96   $180.95   $181.00  
  Purchase #7 $120.46   8.250%   $130.398   $130.40   $130.40   $130.40  
  7 purchase totals = $680.40       $733.5283   $733.53   $733.55   $733.60