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 $45.64   6.284%   $48.508   $48.51   $48.50   $48.50  
  Purchase #2 $217.89   9.214%   $237.9664   $237.97   $237.95   $238.00  
  Purchase #3 $141.99   8.269%   $153.7312   $153.73   $153.75   $153.70  
  Purchase #4 $206.86   5.344%   $217.9146   $217.91   $217.90   $217.90  
  Purchase #5 $100.87   3.109%   $104.006   $104.01   $104.00   $104.00  
  Purchase #6 $85.57   12.766%   $96.4939   $96.49   $96.50   $96.50  
  Purchase #7 $177.83   3.807%   $184.6   $184.60   $184.60   $184.60  
  7 purchase totals = $976.65       $1,043.2201   $1,043.22   $1,043.20   $1,043.20