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	$37.31	11.793%	$41.71	$41.71	$41.70	$41.70
Purchase #2	$230.77	6.320%	$245.3547	$245.35	$245.35	$245.40
Purchase #3	$40.85	12.288%	$45.8696	$45.87	$45.85	$45.90
Purchase #4	$26.30	9.653%	$28.8387	$28.84	$28.85	$28.80
Purchase #5	$94.33	12.296%	$105.9288	$105.93	$105.95	$105.90
Purchase #6	$6.64	7.591%	$7.144	$7.14	$7.15	$7.10
Purchase #7	$222.49	13.150%	$251.7474	$251.75	$251.75	$251.70
7 purchase totals =	$658.69		$726.5932	$726.59	$726.60	$726.50