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	$45.78	7.409%	$49.1718	$49.17	$49.15	$49.20
Purchase #2	$223.34	13.530%	$253.5579	$253.56	$253.55	$253.60
Purchase #3	$166.95	12.624%	$188.0258	$188.03	$188.05	$188.00
Purchase #4	$34.48	9.193%	$37.6497	$37.65	$37.65	$37.60
Purchase #5	$78.70	5.250%	$82.8318	$82.83	$82.85	$82.80
Purchase #6	$237.73	3.829%	$246.8327	$246.83	$246.85	$246.80
Purchase #7	$152.78	3.745%	$158.5016	$158.50	$158.50	$158.50
7 purchase totals =	$939.76		$1,016.5713	$1,016.57	$1,016.60	$1,016.50