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 $185.86   6.323%   $197.6119   $197.61   $197.60   $197.60  
  Purchase #2 $217.82   6.841%   $232.7211   $232.72   $232.70   $232.70  
  Purchase #3 $186.95   9.201%   $204.1513   $204.15   $204.15   $204.20  
  Purchase #4 $241.49   4.480%   $252.3088   $252.31   $252.30   $252.30  
  Purchase #5 $214.97   6.472%   $228.8829   $228.88   $228.90   $228.90  
  Purchase #6 $117.99   12.696%   $132.97   $132.97   $132.95   $133.00  
  Purchase #7 $21.91   5.242%   $23.0585   $23.06   $23.05   $23.10  
  7 purchase totals = $1,186.99       $1,271.7045   $1,271.70   $1,271.65   $1,271.80