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 $230.68   9.778%   $253.2359   $253.24   $253.25   $253.20  
  Purchase #2 $87.82   9.293%   $95.9811   $95.98   $96.00   $96.00  
  Purchase #3 $164.93   8.405%   $178.7924   $178.79   $178.80   $178.80  
  Purchase #4 $100.53   8.727%   $109.3033   $109.30   $109.30   $109.30  
  Purchase #5 $99.33   9.200%   $108.4684   $108.47   $108.45   $108.50  
  Purchase #6 $175.80   9.135%   $191.8593   $191.86   $191.85   $191.90  
  Purchase #7 $210.26   8.873%   $228.9164   $228.92   $228.90   $228.90  
  7 purchase totals = $1,069.35       $1,166.5568   $1,166.56   $1,166.55   $1,166.60