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	$250.72	10.842%	$277.9031	$277.90	$277.90	$277.90
Purchase #2	$96.93	5.148%	$101.92	$101.92	$101.90	$101.90
Purchase #3	$16.91	10.776%	$18.7322	$18.73	$18.75	$18.70
Purchase #4	$173.89	4.762%	$182.1706	$182.17	$182.15	$182.20
Purchase #5	$122.34	10.203%	$134.8224	$134.82	$134.80	$134.80
Purchase #6	$152.56	10.195%	$168.1135	$168.11	$168.10	$168.10
Purchase #7	$117.86	11.468%	$131.3762	$131.38	$131.40	$131.40
7 purchase totals =	$931.21		$1,015.0380	$1,015.03	$1,015.00	$1,015.00