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	$74.45	11.316%	$82.8748	$82.87	$82.85	$82.90
Purchase #2	$130.39	12.236%	$146.3445	$146.34	$146.35	$146.30
Purchase #3	$7.40	9.869%	$8.1303	$8.13	$8.15	$8.10
Purchase #4	$237.62	11.294%	$264.4568	$264.46	$264.45	$264.50
Purchase #5	$71.62	6.462%	$76.2481	$76.25	$76.25	$76.20
Purchase #6	$77.69	6.507%	$82.7453	$82.75	$82.75	$82.70
Purchase #7	$160.52	12.444%	$180.4951	$180.50	$180.50	$180.50
7 purchase totals =	$759.69		$841.2949	$841.30	$841.30	$841.20