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	$249.77	8.310%	$270.5259	$270.53	$270.55	$270.50
Purchase #2	$154.58	9.496%	$169.2589	$169.26	$169.25	$169.30
Purchase #3	$33.72	10.504%	$37.2619	$37.26	$37.25	$37.30
Purchase #4	$213.40	7.462%	$229.3239	$229.32	$229.30	$229.30
Purchase #5	$141.30	4.338%	$147.4296	$147.43	$147.45	$147.40
Purchase #6	$40.66	10.709%	$45.0143	$45.01	$45.00	$45.00
Purchase #7	$158.33	9.205%	$172.9043	$172.90	$172.90	$172.90
7 purchase totals =	$991.76		$1,071.7188	$1,071.71	$1,071.70	$1,071.70