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 $244.77   9.773%   $268.6914   $268.69   $268.70   $268.70  
  Purchase #2 $212.84   12.451%   $239.3407   $239.34   $239.35   $239.30  
  Purchase #3 $44.66   8.394%   $48.4088   $48.41   $48.40   $48.40  
  Purchase #4 $41.96   4.758%   $43.9565   $43.96   $43.95   $44.00  
  Purchase #5 $70.59   8.159%   $76.3494   $76.35   $76.35   $76.30  
  Purchase #6 $250.69   12.742%   $282.6329   $282.63   $282.65   $282.60  
  Purchase #7 $42.57   5.650%   $44.9752   $44.98   $45.00   $45.00  
  7 purchase totals = $908.08       $1,004.3549   $1,004.36   $1,004.40   $1,004.30