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 $228.45   12.120%   $256.1381   $256.14   $256.15   $256.10  
  Purchase #2 $228.66   13.269%   $259.0009   $259.00   $259.00   $259.00  
  Purchase #3 $155.46   12.311%   $174.5987   $174.60   $174.60   $174.60  
  Purchase #4 $173.81   11.517%   $193.8277   $193.83   $193.85   $193.80  
  Purchase #5 $119.85   12.753%   $135.1345   $135.13   $135.15   $135.10  
  Purchase #6 $16.48   8.169%   $17.8263   $17.83   $17.85   $17.80  
  Purchase #7 $146.70   8.657%   $159.3998   $159.40   $159.40   $159.40  
  7 purchase totals = $1,069.41       $1,195.9260   $1,195.93   $1,196.00   $1,195.80