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	$246.55	11.523%	$274.96	$274.96	$274.95	$275.00
Purchase #2	$145.28	4.817%	$152.2781	$152.28	$152.30	$152.30
Purchase #3	$41.98	13.306%	$47.5659	$47.57	$47.55	$47.60
Purchase #4	$78.43	9.613%	$85.9695	$85.97	$85.95	$86.00
Purchase #5	$105.80	11.110%	$117.5544	$117.55	$117.55	$117.60
Purchase #6	$228.30	12.494%	$256.8238	$256.82	$256.80	$256.80
Purchase #7	$125.43	4.841%	$131.5021	$131.50	$131.50	$131.50
7 purchase totals =	$971.77		$1,066.6538	$1,066.65	$1,066.60	$1,066.80