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 $58.99   5.121%   $62.0109   $62.01   $62.00   $62.00  
  Purchase #2 $13.41   13.205%   $15.1808   $15.18   $15.20   $15.20  
  Purchase #3 $148.36   3.523%   $153.5867   $153.59   $153.60   $153.60  
  Purchase #4 $41.85   11.342%   $46.5966   $46.60   $46.60   $46.60  
  Purchase #5 $194.73   3.688%   $201.9116   $201.91   $201.90   $201.90  
  Purchase #6 $79.44   3.265%   $82.0337   $82.03   $82.05   $82.00  
  Purchase #7 $199.91   8.556%   $217.0143   $217.01   $217.00   $217.00  
  7 purchase totals = $736.69       $778.3346   $778.33   $778.35   $778.30