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 $227.53   11.654%   $254.0463   $254.05   $254.05   $254.00  
  Purchase #2 $97.65   3.494%   $101.0619   $101.06   $101.05   $101.10  
  Purchase #3 $208.31   11.776%   $232.8406   $232.84   $232.85   $232.80  
  Purchase #4 $139.92   11.632%   $156.1955   $156.20   $156.20   $156.20  
  Purchase #5 $224.76   13.306%   $254.6666   $254.67   $254.65   $254.70  
  Purchase #6 $143.94   3.440%   $148.8915   $148.89   $148.90   $148.90  
  Purchase #7 $66.81   7.240%   $71.647   $71.65   $71.65   $71.60  
  7 purchase totals = $1,108.92       $1,219.3494   $1,219.36   $1,219.35   $1,219.30