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	$141.62	12.393%	$159.171	$159.17	$159.15	$159.20
Purchase #2	$66.78	6.759%	$71.2937	$71.29	$71.30	$71.30
Purchase #3	$35.95	6.287%	$38.2102	$38.21	$38.20	$38.20
Purchase #4	$27.44	5.271%	$28.8864	$28.89	$28.90	$28.90
Purchase #5	$249.43	12.640%	$280.958	$280.96	$280.95	$281.00
Purchase #6	$123.93	3.867%	$128.7224	$128.72	$128.70	$128.70
Purchase #7	$19.47	4.811%	$20.4067	$20.41	$20.40	$20.40
7 purchase totals =	$664.62		$727.6484	$727.65	$727.60	$727.70