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 $41.32   7.779%   $44.5343   $44.53   $44.55   $44.50  
  Purchase #2 $142.89   7.814%   $154.0554   $154.06   $154.05   $154.10  
  Purchase #3 $237.79   7.433%   $255.4649   $255.46   $255.45   $255.50  
  Purchase #4 $116.75   8.398%   $126.5547   $126.55   $126.55   $126.60  
  Purchase #5 $126.27   8.519%   $137.0269   $137.03   $137.05   $137.00  
  Purchase #6 $190.28   12.549%   $214.1582   $214.16   $214.15   $214.20  
  Purchase #7 $96.66   8.461%   $104.8384   $104.84   $104.85   $104.80  
  7 purchase totals = $951.96       $1,036.6328   $1,036.63   $1,036.65   $1,036.70