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 $210.89   10.410%   $232.8436   $232.84   $232.85   $232.80  
  Purchase #2 $44.29   10.836%   $49.0893   $49.09   $49.10   $49.10  
  Purchase #3 $198.34   10.671%   $219.5049   $219.50   $219.50   $219.50  
  Purchase #4 $58.54   3.483%   $60.5789   $60.58   $60.60   $60.60  
  Purchase #5 $160.31   4.434%   $167.4181   $167.42   $167.40   $167.40  
  Purchase #6 $146.59   8.359%   $158.8435   $158.84   $158.85   $158.80  
  Purchase #7 $127.56   4.741%   $133.6076   $133.61   $133.60   $133.60  
  7 purchase totals = $946.52       $1,021.8859   $1,021.88   $1,021.90   $1,021.80