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	$72.74	7.381%	$78.1089	$78.11	$78.10	$78.10
Purchase #2	$48.38	12.259%	$54.3109	$54.31	$54.30	$54.30
Purchase #3	$185.97	13.208%	$210.5329	$210.53	$210.55	$210.50
Purchase #4	$223.70	7.513%	$240.5066	$240.51	$240.50	$240.50
Purchase #5	$140.84	12.414%	$158.3239	$158.32	$158.30	$158.30
Purchase #6	$138.33	5.140%	$145.4402	$145.44	$145.45	$145.40
Purchase #7	$52.80	10.201%	$58.1861	$58.19	$58.20	$58.20
7 purchase totals =	$862.76		$945.4095	$945.41	$945.40	$945.30