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 $237.41   11.613%   $264.9804   $264.98   $265.00   $265.00  
  Purchase #2 $153.26   3.335%   $158.3712   $158.37   $158.35   $158.40  
  Purchase #3 $135.66   3.395%   $140.2657   $140.27   $140.25   $140.30  
  Purchase #4 $181.59   10.411%   $200.4953   $200.50   $200.50   $200.50  
  Purchase #5 $102.93   12.141%   $115.4267   $115.43   $115.45   $115.40  
  Purchase #6 $79.39   11.478%   $88.5024   $88.50   $88.50   $88.50  
  Purchase #7 $229.26   10.829%   $254.0866   $254.09   $254.10   $254.10  
  7 purchase totals = $1,119.50       $1,222.1283   $1,222.14   $1,222.15   $1,222.20