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 $227.55   7.344%   $244.2613   $244.26   $244.25   $244.30  
  Purchase #2 $89.68   3.302%   $92.6412   $92.64   $92.65   $92.60  
  Purchase #3 $17.52   11.859%   $19.5977   $19.60   $19.60   $19.60  
  Purchase #4 $107.88   6.850%   $115.2698   $115.27   $115.25   $115.30  
  Purchase #5 $93.45   4.327%   $97.4936   $97.49   $97.50   $97.50  
  Purchase #6 $196.95   12.766%   $222.0926   $222.09   $222.10   $222.10  
  Purchase #7 $162.26   6.398%   $172.6414   $172.64   $172.65   $172.60  
  7 purchase totals = $895.29       $963.9976   $963.99   $964.00   $964.00