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 $84.60   10.275%   $93.2927   $93.29   $93.30   $93.30  
  Purchase #2 $164.69   6.545%   $175.469   $175.47   $175.45   $175.50  
  Purchase #3 $159.90   4.642%   $167.3226   $167.32   $167.30   $167.30  
  Purchase #4 $219.72   4.442%   $229.48   $229.48   $229.50   $229.50  
  Purchase #5 $194.35   4.576%   $203.2435   $203.24   $203.25   $203.20  
  Purchase #6 $226.53   11.652%   $252.9253   $252.93   $252.95   $252.90  
  Purchase #7 $250.65   7.838%   $270.2959   $270.30   $270.30   $270.30  
  7 purchase totals = $1,300.44       $1,392.0290   $1,392.03   $1,392.05   $1,392.00