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 $73.42   13.113%   $83.0476   $83.05   $83.05   $83.00  
  Purchase #2 $132.66   10.170%   $146.1515   $146.15   $146.15   $146.20  
  Purchase #3 $120.73   10.812%   $133.7833   $133.78   $133.80   $133.80  
  Purchase #4 $211.81   11.579%   $236.3355   $236.34   $236.35   $236.30  
  Purchase #5 $91.61   5.291%   $96.4571   $96.46   $96.45   $96.50  
  Purchase #6 $26.92   12.832%   $30.3744   $30.37   $30.35   $30.40  
  Purchase #7 $74.59   8.764%   $81.1271   $81.13   $81.15   $81.10  
  7 purchase totals = $731.74       $807.2765   $807.28   $807.30   $807.30