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 $227.57   7.215%   $243.9892   $243.99   $244.00   $244.00  
  Purchase #2 $234.95   13.182%   $265.9211   $265.92   $265.90   $265.90  
  Purchase #3 $76.85   5.115%   $80.7809   $80.78   $80.80   $80.80  
  Purchase #4 $20.47   11.813%   $22.8881   $22.89   $22.90   $22.90  
  Purchase #5 $192.61   10.545%   $212.9207   $212.92   $212.90   $212.90  
  Purchase #6 $40.38   12.452%   $45.4081   $45.41   $45.40   $45.40  
  Purchase #7 $22.85   3.271%   $23.5974   $23.60   $23.60   $23.60  
  7 purchase totals = $815.68       $895.5055   $895.51   $895.50   $895.50