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 $29.80   8.569%   $32.3536   $32.35   $32.35   $32.40  
  Purchase #2 $46.85   3.664%   $48.5666   $48.57   $48.55   $48.60  
  Purchase #3 $127.32   4.841%   $133.4836   $133.48   $133.50   $133.50  
  Purchase #4 $95.32   9.375%   $104.2563   $104.26   $104.25   $104.30  
  Purchase #5 $8.84   11.223%   $9.8321   $9.83   $9.85   $9.80  
  Purchase #6 $241.36   4.335%   $251.823   $251.82   $251.80   $251.80  
  Purchase #7 $197.86   11.495%   $220.604   $220.60   $220.60   $220.60  
  7 purchase totals = $747.35       $800.9192   $800.91   $800.90   $801.00