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 $126.94   6.450%   $135.1276   $135.13   $135.15   $135.10  
  Purchase #2 $228.38   13.660%   $259.5767   $259.58   $259.60   $259.60  
  Purchase #3 $60.31   3.113%   $62.1875   $62.19   $62.20   $62.20  
  Purchase #4 $237.34   5.782%   $251.063   $251.06   $251.05   $251.10  
  Purchase #5 $77.25   7.812%   $83.2848   $83.28   $83.30   $83.30  
  Purchase #6 $75.94   12.105%   $85.1325   $85.13   $85.15   $85.10  
  Purchase #7 $163.79   8.354%   $177.473   $177.47   $177.45   $177.50  
  7 purchase totals = $969.95       $1,053.8451   $1,053.84   $1,053.90   $1,053.90