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	$154.93	11.206%	$172.2915	$172.29	$172.30	$172.30
Purchase #2	$37.49	13.731%	$42.6378	$42.64	$42.65	$42.60
Purchase #3	$79.93	4.753%	$83.7291	$83.73	$83.75	$83.70
Purchase #4	$162.30	12.606%	$182.7595	$182.76	$182.75	$182.80
Purchase #5	$92.32	4.364%	$96.3488	$96.35	$96.35	$96.30
Purchase #6	$247.47	11.471%	$275.8573	$275.86	$275.85	$275.90
Purchase #7	$146.54	9.342%	$160.2298	$160.23	$160.25	$160.20
7 purchase totals =	$920.98		$1,013.8538	$1,013.86	$1,013.90	$1,013.80