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	$84.91	6.688%	$90.5888	$90.59	$90.60	$90.60
Purchase #2	$51.96	8.415%	$56.3324	$56.33	$56.35	$56.30
Purchase #3	$239.58	12.444%	$269.3933	$269.39	$269.40	$269.40
Purchase #4	$37.61	9.388%	$41.1408	$41.14	$41.15	$41.10
Purchase #5	$39.97	4.211%	$41.6531	$41.65	$41.65	$41.70
Purchase #6	$90.60	6.126%	$96.1502	$96.15	$96.15	$96.20
Purchase #7	$147.34	13.448%	$167.1543	$167.15	$167.15	$167.20
7 purchase totals =	$691.97		$762.4129	$762.40	$762.45	$762.50