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 $201.48   6.811%   $215.2028   $215.20   $215.20   $215.20  
  Purchase #2 $249.79   5.154%   $262.6642   $262.66   $262.65   $262.70  
  Purchase #3 $186.45   11.692%   $208.2497   $208.25   $208.25   $208.20  
  Purchase #4 $72.92   12.297%   $81.887   $81.89   $81.90   $81.90  
  Purchase #5 $65.26   3.420%   $67.4919   $67.49   $67.50   $67.50  
  Purchase #6 $30.49   6.375%   $32.4337   $32.43   $32.45   $32.40  
  Purchase #7 $210.92   4.559%   $220.5358   $220.54   $220.55   $220.50  
  7 purchase totals = $1,017.31       $1,088.4651   $1,088.46   $1,088.50   $1,088.40