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 $233.57   5.347%   $246.059   $246.06   $246.05   $246.10  
  Purchase #2 $69.52   3.311%   $71.8218   $71.82   $71.80   $71.80  
  Purchase #3 $204.30   11.836%   $228.4809   $228.48   $228.50   $228.50  
  Purchase #4 $159.60   3.105%   $164.5556   $164.56   $164.55   $164.60  
  Purchase #5 $180.41   9.759%   $198.0162   $198.02   $198.00   $198.00  
  Purchase #6 $40.48   9.817%   $44.4539   $44.45   $44.45   $44.50  
  Purchase #7 $93.75   8.711%   $101.9166   $101.92   $101.90   $101.90  
  7 purchase totals = $981.63       $1,055.3040   $1,055.31   $1,055.25   $1,055.40