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	$160.91	4.594%	$168.3022	$168.30	$168.30	$168.30
Purchase #2	$201.84	5.687%	$213.3186	$213.32	$213.30	$213.30
Purchase #3	$56.25	11.117%	$62.5033	$62.50	$62.50	$62.50
Purchase #4	$200.54	11.257%	$223.1148	$223.11	$223.10	$223.10
Purchase #5	$145.53	9.502%	$159.3583	$159.36	$159.35	$159.40
Purchase #6	$180.31	6.634%	$192.2718	$192.27	$192.25	$192.30
Purchase #7	$245.95	13.764%	$279.8026	$279.80	$279.80	$279.80
7 purchase totals =	$1,191.33		$1,298.6716	$1,298.66	$1,298.60	$1,298.70