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	$90.80	9.210%	$99.1627	$99.16	$99.15	$99.20
Purchase #2	$93.86	5.184%	$98.7257	$98.73	$98.75	$98.70
Purchase #3	$71.69	9.867%	$78.7637	$78.76	$78.75	$78.80
Purchase #4	$192.39	9.226%	$210.1399	$210.14	$210.15	$210.10
Purchase #5	$69.39	8.675%	$75.4096	$75.41	$75.40	$75.40
Purchase #6	$214.33	4.172%	$223.2718	$223.27	$223.25	$223.30
Purchase #7	$165.67	8.618%	$179.9474	$179.95	$179.95	$179.90
7 purchase totals =	$898.13		$965.4208	$965.42	$965.40	$965.40