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	$51.30	5.385%	$54.0625	$54.06	$54.05	$54.10
Purchase #2	$161.97	12.675%	$182.4997	$182.50	$182.50	$182.50
Purchase #3	$155.37	7.354%	$166.7959	$166.80	$166.80	$166.80
Purchase #4	$96.74	12.785%	$109.1082	$109.11	$109.10	$109.10
Purchase #5	$244.90	10.787%	$271.3174	$271.32	$271.30	$271.30
Purchase #6	$44.41	5.212%	$46.7246	$46.72	$46.70	$46.70
Purchase #7	$247.56	11.161%	$275.1902	$275.19	$275.20	$275.20
7 purchase totals =	$1,002.25		$1,105.6985	$1,105.70	$1,105.65	$1,105.70