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 $113.36   5.716%   $119.8397   $119.84   $119.85   $119.80  
  Purchase #2 $224.32   13.180%   $253.8854   $253.89   $253.90   $253.90  
  Purchase #3 $212.41   4.686%   $222.3635   $222.36   $222.35   $222.40  
  Purchase #4 $30.98   7.742%   $33.3785   $33.38   $33.40   $33.40  
  Purchase #5 $221.48   11.842%   $247.7077   $247.71   $247.70   $247.70  
  Purchase #6 $187.67   7.559%   $201.856   $201.86   $201.85   $201.90  
  Purchase #7 $60.53   11.696%   $67.6096   $67.61   $67.60   $67.60  
  7 purchase totals = $1,050.75       $1,146.6404   $1,146.65   $1,146.65   $1,146.70