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 $30.71   13.108%   $34.7355   $34.74   $34.75   $34.70  
  Purchase #2 $55.45   9.314%   $60.6146   $60.61   $60.60   $60.60  
  Purchase #3 $219.95   5.520%   $232.0912   $232.09   $232.10   $232.10  
  Purchase #4 $76.75   13.789%   $87.3331   $87.33   $87.35   $87.30  
  Purchase #5 $209.25   7.212%   $224.3411   $224.34   $224.35   $224.30  
  Purchase #6 $36.66   11.532%   $40.8876   $40.89   $40.90   $40.90  
  Purchase #7 $66.80   12.572%   $75.1981   $75.20   $75.20   $75.20  
  7 purchase totals = $695.57       $755.2012   $755.20   $755.25   $755.10