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 $247.41   11.572%   $276.0403   $276.04   $276.05   $276.00  
  Purchase #2 $72.78   3.195%   $75.1053   $75.11   $75.10   $75.10  
  Purchase #3 $92.62   6.866%   $98.9793   $98.98   $99.00   $99.00  
  Purchase #4 $116.93   6.414%   $124.4299   $124.43   $124.45   $124.40  
  Purchase #5 $208.78   6.589%   $222.5365   $222.54   $222.55   $222.50  
  Purchase #6 $10.98   8.178%   $11.8779   $11.88   $11.90   $11.90  
  Purchase #7 $84.89   9.243%   $92.7364   $92.74   $92.75   $92.70  
  7 purchase totals = $834.39       $901.7056   $901.72   $901.80   $901.60