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	$77.61	4.864%	$81.385	$81.39	$81.40	$81.40
Purchase #2	$76.43	10.549%	$84.4926	$84.49	$84.50	$84.50
Purchase #3	$143.59	9.404%	$157.0932	$157.09	$157.10	$157.10
Purchase #4	$79.77	12.180%	$89.486	$89.49	$89.50	$89.50
Purchase #5	$250.78	11.628%	$279.9407	$279.94	$279.95	$279.90
Purchase #6	$83.98	6.388%	$89.3446	$89.34	$89.35	$89.30
Purchase #7	$69.89	8.503%	$75.8327	$75.83	$75.85	$75.80
7 purchase totals =	$782.05		$857.5748	$857.57	$857.65	$857.50