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	$139.82	4.541%	$146.1692	$146.17	$146.15	$146.20
Purchase #2	$205.45	11.633%	$229.35	$229.35	$229.35	$229.40
Purchase #3	$61.64	7.525%	$66.2784	$66.28	$66.30	$66.30
Purchase #4	$243.72	12.386%	$273.9072	$273.91	$273.90	$273.90
Purchase #5	$219.32	4.838%	$229.9307	$229.93	$229.95	$229.90
Purchase #6	$250.47	5.600%	$264.4963	$264.50	$264.50	$264.50
Purchase #7	$61.62	6.158%	$65.4146	$65.41	$65.40	$65.40
7 purchase totals =	$1,182.04		$1,275.5464	$1,275.55	$1,275.55	$1,275.60