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	$117.35	13.183%	$132.8203	$132.82	$132.80	$132.80
Purchase #2	$245.51	11.212%	$273.0366	$273.04	$273.05	$273.00
Purchase #3	$77.43	8.233%	$83.8048	$83.80	$83.80	$83.80
Purchase #4	$154.46	12.559%	$173.8586	$173.86	$173.85	$173.90
Purchase #5	$99.52	3.791%	$103.2928	$103.29	$103.30	$103.30
Purchase #6	$213.94	4.664%	$223.9182	$223.92	$223.90	$223.90
Purchase #7	$98.65	11.463%	$109.9582	$109.96	$109.95	$110.00
7 purchase totals =	$1,006.86		$1,100.6895	$1,100.69	$1,100.65	$1,100.70