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 $41.34   8.447%   $44.832   $44.83   $44.85   $44.80  
  Purchase #2 $234.84   9.395%   $256.9032   $256.90   $256.90   $256.90  
  Purchase #3 $224.54   4.821%   $235.3651   $235.37   $235.35   $235.40  
  Purchase #4 $104.47   5.763%   $110.4906   $110.49   $110.50   $110.50  
  Purchase #5 $162.89   8.690%   $177.0451   $177.05   $177.05   $177.00  
  Purchase #6 $128.46   8.630%   $139.5461   $139.55   $139.55   $139.50  
  Purchase #7 $117.28   8.845%   $127.6534   $127.65   $127.65   $127.70  
  7 purchase totals = $1,013.82       $1,091.8355   $1,091.84   $1,091.85   $1,091.80