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	$232.29	11.837%	$259.7862	$259.79	$259.80	$259.80
Purchase #2	$162.28	6.319%	$172.5345	$172.53	$172.55	$172.50
Purchase #3	$159.30	6.563%	$169.7549	$169.75	$169.75	$169.80
Purchase #4	$39.94	12.800%	$45.0523	$45.05	$45.05	$45.10
Purchase #5	$37.66	6.384%	$40.0642	$40.06	$40.05	$40.10
Purchase #6	$243.39	8.820%	$264.857	$264.86	$264.85	$264.90
Purchase #7	$45.71	10.530%	$50.5233	$50.52	$50.50	$50.50
7 purchase totals =	$920.57		$1,002.5724	$1,002.56	$1,002.55	$1,002.70