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	$73.54	6.263%	$78.1458	$78.15	$78.15	$78.10
Purchase #2	$116.92	9.741%	$128.3092	$128.31	$128.30	$128.30
Purchase #3	$109.87	12.414%	$123.5093	$123.51	$123.50	$123.50
Purchase #4	$159.55	3.243%	$164.7242	$164.72	$164.70	$164.70
Purchase #5	$58.54	9.426%	$64.058	$64.06	$64.05	$64.10
Purchase #6	$5.80	11.841%	$6.4868	$6.49	$6.50	$6.50
Purchase #7	$171.47	10.242%	$189.032	$189.03	$189.05	$189.00
7 purchase totals =	$695.69		$754.2653	$754.27	$754.25	$754.20