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	$70.47	8.303%	$76.3211	$76.32	$76.30	$76.30
Purchase #2	$98.62	13.459%	$111.8933	$111.89	$111.90	$111.90
Purchase #3	$58.96	6.449%	$62.7623	$62.76	$62.75	$62.80
Purchase #4	$157.36	6.214%	$167.1384	$167.14	$167.15	$167.10
Purchase #5	$25.34	3.851%	$26.3158	$26.32	$26.30	$26.30
Purchase #6	$13.59	11.747%	$15.1864	$15.19	$15.20	$15.20
Purchase #7	$104.87	6.123%	$111.2912	$111.29	$111.30	$111.30
7 purchase totals =	$529.21		$570.9085	$570.91	$570.90	$570.90