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 $98.66   6.359%   $104.9338   $104.93   $104.95   $104.90  
  Purchase #2 $227.89   5.243%   $239.8383   $239.84   $239.85   $239.80  
  Purchase #3 $53.66   11.687%   $59.9312   $59.93   $59.95   $59.90  
  Purchase #4 $62.92   8.782%   $68.4456   $68.45   $68.45   $68.40  
  Purchase #5 $137.95   11.522%   $153.8446   $153.84   $153.85   $153.80  
  Purchase #6 $190.41   11.515%   $212.3357   $212.34   $212.35   $212.30  
  Purchase #7 $94.92   10.726%   $105.1011   $105.10   $105.10   $105.10  
  7 purchase totals = $866.41       $944.4303   $944.43   $944.50   $944.20