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 $217.73   7.466%   $233.9857   $233.99   $234.00   $234.00  
  Purchase #2 $36.65   3.317%   $37.8657   $37.87   $37.85   $37.90  
  Purchase #3 $16.93   4.162%   $17.6346   $17.63   $17.65   $17.60  
  Purchase #4 $230.92   3.184%   $238.2725   $238.27   $238.25   $238.30  
  Purchase #5 $124.63   13.460%   $141.4052   $141.41   $141.40   $141.40  
  Purchase #6 $116.98   7.132%   $125.323   $125.32   $125.30   $125.30  
  Purchase #7 $81.40   12.140%   $91.282   $91.28   $91.30   $91.30  
  7 purchase totals = $825.24       $885.7687   $885.77   $885.75   $885.80