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	$124.55	6.650%	$132.8326	$132.83	$132.85	$132.80
Purchase #2	$92.41	4.812%	$96.8568	$96.86	$96.85	$96.90
Purchase #3	$159.65	9.688%	$175.1169	$175.12	$175.10	$175.10
Purchase #4	$128.34	4.674%	$134.3386	$134.34	$134.35	$134.30
Purchase #5	$70.45	3.123%	$72.6502	$72.65	$72.65	$72.70
Purchase #6	$48.75	11.409%	$54.3119	$54.31	$54.30	$54.30
Purchase #7	$160.91	11.668%	$179.685	$179.69	$179.70	$179.70
7 purchase totals =	$785.06		$845.7920	$845.80	$845.80	$845.80