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 $248.56   11.201%   $276.4012   $276.40   $276.40   $276.40  
  Purchase #2 $191.55   4.809%   $200.7616   $200.76   $200.75   $200.80  
  Purchase #3 $125.85   3.870%   $130.7204   $130.72   $130.70   $130.70  
  Purchase #4 $86.62   8.147%   $93.6769   $93.68   $93.70   $93.70  
  Purchase #5 $247.34   11.342%   $275.3933   $275.39   $275.40   $275.40  
  Purchase #6 $130.47   13.828%   $148.5114   $148.51   $148.50   $148.50  
  Purchase #7 $218.37   4.719%   $228.6749   $228.67   $228.65   $228.70  
  7 purchase totals = $1,248.76       $1,354.1397   $1,354.13   $1,354.10   $1,354.20