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 $39.95   13.390%   $45.2993   $45.30   $45.30   $45.30  
  Purchase #2 $201.98   10.130%   $222.4406   $222.44   $222.45   $222.40  
  Purchase #3 $44.56   12.334%   $50.056   $50.06   $50.05   $50.10  
  Purchase #4 $200.60   3.662%   $207.946   $207.95   $207.95   $207.90  
  Purchase #5 $73.30   5.388%   $77.2494   $77.25   $77.25   $77.20  
  Purchase #6 $48.28   8.635%   $52.449   $52.45   $52.45   $52.40  
  Purchase #7 $226.63   5.211%   $238.4397   $238.44   $238.45   $238.40  
  7 purchase totals = $835.30       $893.8800   $893.89   $893.90   $893.70