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 $192.27   12.870%   $217.0151   $217.02   $217.00   $217.00  
  Purchase #2 $231.42   9.847%   $254.2079   $254.21   $254.20   $254.20  
  Purchase #3 $22.55   6.298%   $23.9702   $23.97   $23.95   $24.00  
  Purchase #4 $40.98   5.776%   $43.347   $43.35   $43.35   $43.30  
  Purchase #5 $98.95   12.516%   $111.3346   $111.33   $111.35   $111.30  
  Purchase #6 $128.87   3.166%   $132.95   $132.95   $132.95   $133.00  
  Purchase #7 $175.77   4.137%   $183.0416   $183.04   $183.05   $183.00  
  7 purchase totals = $890.81       $965.8664   $965.87   $965.85   $965.80