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 $47.50   11.161%   $52.8015   $52.80   $52.80   $52.80  
  Purchase #2 $32.33   13.429%   $36.6716   $36.67   $36.65   $36.70  
  Purchase #3 $227.68   5.761%   $240.7966   $240.80   $240.80   $240.80  
  Purchase #4 $243.56   12.484%   $273.966   $273.97   $273.95   $274.00  
  Purchase #5 $47.71   11.858%   $53.3675   $53.37   $53.35   $53.40  
  Purchase #6 $186.94   13.311%   $211.8236   $211.82   $211.80   $211.80  
  Purchase #7 $23.81   10.784%   $26.3777   $26.38   $26.40   $26.40  
  7 purchase totals = $809.53       $895.8045   $895.81   $895.75   $895.90