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	$209.36	11.342%	$233.1056	$233.11	$233.10	$233.10
Purchase #2	$130.31	12.570%	$146.69	$146.69	$146.70	$146.70
Purchase #3	$87.56	10.613%	$96.8527	$96.85	$96.85	$96.90
Purchase #4	$49.28	12.651%	$55.5144	$55.51	$55.50	$55.50
Purchase #5	$139.78	11.838%	$156.3272	$156.33	$156.35	$156.30
Purchase #6	$85.66	5.307%	$90.206	$90.21	$90.20	$90.20
Purchase #7	$130.48	13.804%	$148.4915	$148.49	$148.50	$148.50
7 purchase totals =	$832.43		$927.1874	$927.19	$927.20	$927.20