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 $192.56   11.547%   $214.7949   $214.79   $214.80   $214.80  
  Purchase #2 $64.56   10.288%   $71.2019   $71.20   $71.20   $71.20  
  Purchase #3 $160.51   9.485%   $175.7344   $175.73   $175.75   $175.70  
  Purchase #4 $117.83   9.385%   $128.8883   $128.89   $128.90   $128.90  
  Purchase #5 $190.52   9.565%   $208.7432   $208.74   $208.75   $208.70  
  Purchase #6 $246.87   5.195%   $259.6949   $259.69   $259.70   $259.70  
  Purchase #7 $102.55   7.670%   $110.4156   $110.42   $110.40   $110.40  
  7 purchase totals = $1,075.40       $1,169.4732   $1,169.46   $1,169.50   $1,169.40