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	$97.55	6.427%	$103.8195	$103.82	$103.80	$103.80
Purchase #2	$221.34	10.227%	$243.9764	$243.98	$244.00	$244.00
Purchase #3	$153.55	3.464%	$158.869	$158.87	$158.85	$158.90
Purchase #4	$33.79	11.185%	$37.5694	$37.57	$37.55	$37.60
Purchase #5	$245.85	11.636%	$274.4571	$274.46	$274.45	$274.50
Purchase #6	$216.77	12.285%	$243.4002	$243.40	$243.40	$243.40
Purchase #7	$178.66	9.757%	$196.0919	$196.09	$196.10	$196.10
7 purchase totals =	$1,147.51		$1,258.1835	$1,258.19	$1,258.15	$1,258.30