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 $118.70   6.189%   $126.0463   $126.05   $126.05   $126.00  
  Purchase #2 $195.81   4.489%   $204.5999   $204.60   $204.60   $204.60  
  Purchase #3 $77.50   8.616%   $84.1774   $84.18   $84.20   $84.20  
  Purchase #4 $219.31   12.739%   $247.2479   $247.25   $247.25   $247.20  
  Purchase #5 $231.80   11.242%   $257.859   $257.86   $257.85   $257.90  
  Purchase #6 $160.46   8.150%   $173.5375   $173.54   $173.55   $173.50  
  Purchase #7 $117.50   9.710%   $128.9093   $128.91   $128.90   $128.90  
  7 purchase totals = $1,121.08       $1,222.3773   $1,222.39   $1,222.40   $1,222.30