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	$6.63	13.162%	$7.5026	$7.50	$7.50	$7.50
Purchase #2	$240.93	9.637%	$264.1484	$264.15	$264.15	$264.10
Purchase #3	$149.73	12.545%	$168.5136	$168.51	$168.50	$168.50
Purchase #4	$250.38	12.518%	$281.7226	$281.72	$281.70	$281.70
Purchase #5	$100.50	10.104%	$110.6545	$110.65	$110.65	$110.70
Purchase #6	$64.73	4.251%	$67.4817	$67.48	$67.50	$67.50
Purchase #7	$74.39	10.488%	$82.192	$82.19	$82.20	$82.20
7 purchase totals =	$887.29		$982.2154	$982.20	$982.20	$982.20