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	$239.45	12.458%	$269.2807	$269.28	$269.30	$269.30
Purchase #2	$26.31	6.836%	$28.1086	$28.11	$28.10	$28.10
Purchase #3	$62.82	7.137%	$67.3035	$67.30	$67.30	$67.30
Purchase #4	$193.48	10.444%	$213.6871	$213.69	$213.70	$213.70
Purchase #5	$11.96	10.857%	$13.2585	$13.26	$13.25	$13.30
Purchase #6	$98.25	13.694%	$111.7044	$111.70	$111.70	$111.70
Purchase #7	$225.29	13.141%	$254.8954	$254.90	$254.90	$254.90
7 purchase totals =	$857.56		$958.2382	$958.24	$958.25	$958.30