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	$62.89	13.409%	$71.3229	$71.32	$71.30	$71.30
Purchase #2	$120.45	7.690%	$129.7126	$129.71	$129.70	$129.70
Purchase #3	$131.95	7.321%	$141.6101	$141.61	$141.60	$141.60
Purchase #4	$104.73	3.244%	$108.1274	$108.13	$108.15	$108.10
Purchase #5	$112.63	4.216%	$117.3785	$117.38	$117.40	$117.40
Purchase #6	$222.75	11.408%	$248.1613	$248.16	$248.15	$248.20
Purchase #7	$157.64	4.154%	$164.1884	$164.19	$164.20	$164.20
7 purchase totals =	$913.04		$980.5012	$980.50	$980.50	$980.50