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 $10.39   12.231%   $11.6608   $11.66   $11.65   $11.70  
  Purchase #2 $244.36   8.816%   $265.9028   $265.90   $265.90   $265.90  
  Purchase #3 $146.44   4.422%   $152.9156   $152.92   $152.90   $152.90  
  Purchase #4 $203.64   7.149%   $218.1982   $218.20   $218.20   $218.20  
  Purchase #5 $163.66   3.250%   $168.979   $168.98   $169.00   $169.00  
  Purchase #6 $34.80   9.195%   $37.9999   $38.00   $38.00   $38.00  
  Purchase #7 $168.63   10.863%   $186.9483   $186.95   $186.95   $186.90  
  7 purchase totals = $971.92       $1,042.6046   $1,042.61   $1,042.60   $1,042.60