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	$243.34	12.439%	$273.6091	$273.61	$273.60	$273.60
Purchase #2	$217.27	10.633%	$240.3723	$240.37	$240.35	$240.40
Purchase #3	$61.84	13.821%	$70.3869	$70.39	$70.40	$70.40
Purchase #4	$25.55	6.480%	$27.2056	$27.21	$27.20	$27.20
Purchase #5	$60.55	11.399%	$67.4521	$67.45	$67.45	$67.50
Purchase #6	$53.63	7.372%	$57.5836	$57.58	$57.60	$57.60
Purchase #7	$237.84	13.737%	$270.5121	$270.51	$270.50	$270.50
7 purchase totals =	$900.02		$1,007.1217	$1,007.12	$1,007.10	$1,007.20