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 $179.49   13.797%   $204.2542   $204.25   $204.25   $204.30  
  Purchase #2 $96.61   8.179%   $104.5117   $104.51   $104.50   $104.50  
  Purchase #3 $10.40   6.811%   $11.1083   $11.11   $11.10   $11.10  
  Purchase #4 $50.47   11.358%   $56.2024   $56.20   $56.20   $56.20  
  Purchase #5 $217.29   12.590%   $244.6468   $244.65   $244.65   $244.60  
  Purchase #6 $125.61   6.348%   $133.5837   $133.58   $133.60   $133.60  
  Purchase #7 $197.41   10.251%   $217.6465   $217.65   $217.65   $217.60  
  7 purchase totals = $877.28       $971.9536   $971.95   $971.95   $971.90