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 $217.84   7.501%   $234.1802   $234.18   $234.20   $234.20  
  Purchase #2 $222.33   9.520%   $243.4958   $243.50   $243.50   $243.50  
  Purchase #3 $92.66   13.242%   $104.93   $104.93   $104.95   $104.90  
  Purchase #4 $124.36   9.411%   $136.0635   $136.06   $136.05   $136.10  
  Purchase #5 $201.42   13.406%   $228.4224   $228.42   $228.40   $228.40  
  Purchase #6 $61.55   5.821%   $65.1328   $65.13   $65.15   $65.10  
  Purchase #7 $241.68   7.178%   $259.0278   $259.03   $259.05   $259.00  
  7 purchase totals = $1,161.84       $1,271.2525   $1,271.25   $1,271.30   $1,271.20