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 $218.53   8.234%   $236.5238   $236.52   $236.50   $236.50  
  Purchase #2 $162.85   4.826%   $170.7091   $170.71   $170.70   $170.70  
  Purchase #3 $226.66   6.470%   $241.3249   $241.32   $241.30   $241.30  
  Purchase #4 $132.64   5.164%   $139.4895   $139.49   $139.50   $139.50  
  Purchase #5 $239.48   9.572%   $262.403   $262.40   $262.40   $262.40  
  Purchase #6 $210.87   10.255%   $232.4947   $232.49   $232.50   $232.50  
  Purchase #7 $21.54   12.705%   $24.2767   $24.28   $24.30   $24.30  
  7 purchase totals = $1,212.57       $1,307.2217   $1,307.21   $1,307.20   $1,307.20