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	$72.39	13.834%	$82.4044	$82.40	$82.40	$82.40
Purchase #2	$120.72	11.334%	$134.4024	$134.40	$134.40	$134.40
Purchase #3	$56.58	9.310%	$61.8476	$61.85	$61.85	$61.80
Purchase #4	$227.28	3.681%	$235.6462	$235.65	$235.65	$235.60
Purchase #5	$18.51	4.413%	$19.3268	$19.33	$19.35	$19.30
Purchase #6	$134.32	5.611%	$141.8567	$141.86	$141.85	$141.90
Purchase #7	$223.51	9.522%	$244.7926	$244.79	$244.80	$244.80
7 purchase totals =	$853.31		$920.2767	$920.28	$920.30	$920.20