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	$71.44	9.842%	$78.4711	$78.47	$78.45	$78.50
Purchase #2	$26.28	7.518%	$28.2557	$28.26	$28.25	$28.30
Purchase #3	$235.82	8.320%	$255.4402	$255.44	$255.45	$255.40
Purchase #4	$45.34	13.727%	$51.5638	$51.56	$51.55	$51.60
Purchase #5	$50.86	5.490%	$53.6522	$53.65	$53.65	$53.70
Purchase #6	$117.46	6.603%	$125.2159	$125.22	$125.20	$125.20
Purchase #7	$180.40	10.221%	$198.8387	$198.84	$198.85	$198.80
7 purchase totals =	$727.60		$791.4376	$791.44	$791.40	$791.50