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	$234.28	11.550%	$261.3393	$261.34	$261.35	$261.30
Purchase #2	$207.62	6.496%	$221.107	$221.11	$221.10	$221.10
Purchase #3	$50.90	3.789%	$52.8286	$52.83	$52.85	$52.80
Purchase #4	$16.85	11.701%	$18.8216	$18.82	$18.80	$18.80
Purchase #5	$51.62	13.705%	$58.6945	$58.69	$58.70	$58.70
Purchase #6	$40.45	11.700%	$45.1827	$45.18	$45.20	$45.20
Purchase #7	$53.60	4.209%	$55.856	$55.86	$55.85	$55.90
7 purchase totals =	$655.32		$713.8297	$713.83	$713.85	$713.80