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 $89.63   5.836%   $94.8608   $94.86   $94.85   $94.90  
  Purchase #2 $46.69   10.752%   $51.7101   $51.71   $51.70   $51.70  
  Purchase #3 $249.78   13.417%   $283.293   $283.29   $283.30   $283.30  
  Purchase #4 $209.46   5.489%   $220.9573   $220.96   $220.95   $221.00  
  Purchase #5 $168.40   12.458%   $189.3793   $189.38   $189.40   $189.40  
  Purchase #6 $158.56   11.123%   $176.1966   $176.20   $176.20   $176.20  
  Purchase #7 $11.33   5.693%   $11.975   $11.98   $12.00   $12.00  
  7 purchase totals = $933.85       $1,028.3721   $1,028.38   $1,028.40   $1,028.50