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 $244.95   12.763%   $276.213   $276.21   $276.20   $276.20  
  Purchase #2 $160.40   5.801%   $169.7048   $169.70   $169.70   $169.70  
  Purchase #3 $146.99   11.470%   $163.8498   $163.85   $163.85   $163.80  
  Purchase #4 $246.94   10.445%   $272.7329   $272.73   $272.75   $272.70  
  Purchase #5 $127.29   6.550%   $135.6275   $135.63   $135.65   $135.60  
  Purchase #6 $177.90   8.667%   $193.3186   $193.32   $193.30   $193.30  
  Purchase #7 $232.68   12.702%   $262.235   $262.24   $262.25   $262.20  
  7 purchase totals = $1,337.15       $1,473.6816   $1,473.68   $1,473.70   $1,473.50