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 $193.27   11.252%   $215.0167   $215.02   $215.00   $215.00  
  Purchase #2 $112.48   3.187%   $116.0647   $116.06   $116.05   $116.10  
  Purchase #3 $109.64   12.829%   $123.7057   $123.71   $123.70   $123.70  
  Purchase #4 $62.84   9.531%   $68.8293   $68.83   $68.85   $68.80  
  Purchase #5 $162.45   6.518%   $173.0385   $173.04   $173.05   $173.00  
  Purchase #6 $249.56   9.466%   $273.1833   $273.18   $273.20   $273.20  
  Purchase #7 $63.26   7.488%   $67.9969   $68.00   $68.00   $68.00  
  7 purchase totals = $953.50       $1,037.8351   $1,037.84   $1,037.85   $1,037.80