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 $95.40   12.540%   $107.3632   $107.36   $107.35   $107.40  
  Purchase #2 $200.39   4.811%   $210.0308   $210.03   $210.05   $210.00  
  Purchase #3 $118.84   5.478%   $125.3501   $125.35   $125.35   $125.40  
  Purchase #4 $96.37   10.508%   $106.4966   $106.50   $106.50   $106.50  
  Purchase #5 $100.43   3.653%   $104.0987   $104.10   $104.10   $104.10  
  Purchase #6 $66.26   12.252%   $74.3782   $74.38   $74.40   $74.40  
  Purchase #7 $113.44   6.333%   $120.6242   $120.62   $120.60   $120.60  
  7 purchase totals = $791.13       $848.3418   $848.34   $848.35   $848.40