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 $152.26   7.732%   $164.0327   $164.03   $164.05   $164.00  
  Purchase #2 $243.52   8.352%   $263.8588   $263.86   $263.85   $263.90  
  Purchase #3 $214.81   4.355%   $224.165   $224.17   $224.15   $224.20  
  Purchase #4 $196.47   11.388%   $218.844   $218.84   $218.85   $218.80  
  Purchase #5 $74.37   11.202%   $82.7009   $82.70   $82.70   $82.70  
  Purchase #6 $195.83   12.131%   $219.5861   $219.59   $219.60   $219.60  
  Purchase #7 $146.61   3.431%   $151.6402   $151.64   $151.65   $151.60  
  7 purchase totals = $1,223.87       $1,324.8277   $1,324.83   $1,324.85   $1,324.80