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 $94.72   10.138%   $104.3227   $104.32   $104.30   $104.30  
  Purchase #2 $221.51   5.327%   $233.3098   $233.31   $233.30   $233.30  
  Purchase #3 $172.96   7.469%   $185.8784   $185.88   $185.90   $185.90  
  Purchase #4 $25.99   9.615%   $28.4889   $28.49   $28.50   $28.50  
  Purchase #5 $106.31   12.549%   $119.6508   $119.65   $119.65   $119.70  
  Purchase #6 $194.26   3.287%   $200.6453   $200.65   $200.65   $200.60  
  Purchase #7 $43.63   8.560%   $47.3647   $47.36   $47.35   $47.40  
  7 purchase totals = $859.38       $919.6606   $919.66   $919.65   $919.70