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 $220.66   11.628%   $246.3183   $246.32   $246.30   $246.30  
  Purchase #2 $244.67   8.261%   $264.8822   $264.88   $264.90   $264.90  
  Purchase #3 $171.77   5.275%   $180.8309   $180.83   $180.85   $180.80  
  Purchase #4 $83.25   11.137%   $92.5216   $92.52   $92.50   $92.50  
  Purchase #5 $36.69   11.821%   $41.0271   $41.03   $41.05   $41.00  
  Purchase #6 $176.40   8.555%   $191.491   $191.49   $191.50   $191.50  
  Purchase #7 $10.99   3.116%   $11.3324   $11.33   $11.35   $11.30  
  7 purchase totals = $944.43       $1,028.4035   $1,028.40   $1,028.45   $1,028.30