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	$117.25	11.829%	$131.1195	$131.12	$131.10	$131.10
Purchase #2	$124.75	8.276%	$135.0743	$135.07	$135.05	$135.10
Purchase #3	$75.67	3.852%	$78.5848	$78.58	$78.60	$78.60
Purchase #4	$155.50	11.425%	$173.2659	$173.27	$173.25	$173.30
Purchase #5	$147.55	13.782%	$167.8853	$167.89	$167.90	$167.90
Purchase #6	$185.88	13.117%	$210.2619	$210.26	$210.25	$210.30
Purchase #7	$72.95	13.175%	$82.5612	$82.56	$82.55	$82.60
7 purchase totals =	$879.55		$978.7529	$978.75	$978.70	$978.90