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 $53.41   11.220%   $59.4026   $59.40   $59.40   $59.40  
  Purchase #2 $150.29   12.423%   $168.9605   $168.96   $168.95   $169.00  
  Purchase #3 $114.96   9.150%   $125.4788   $125.48   $125.50   $125.50  
  Purchase #4 $140.72   11.703%   $157.1885   $157.19   $157.20   $157.20  
  Purchase #5 $163.90   5.253%   $172.5097   $172.51   $172.50   $172.50  
  Purchase #6 $217.39   6.393%   $231.2877   $231.29   $231.30   $231.30  
  Purchase #7 $93.25   13.825%   $106.1418   $106.14   $106.15   $106.10  
  7 purchase totals = $933.92       $1,020.9696   $1,020.97   $1,021.00   $1,021.00