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	$230.35	8.327%	$249.5312	$249.53	$249.55	$249.50
Purchase #2	$250.75	9.800%	$275.3235	$275.32	$275.30	$275.30
Purchase #3	$41.36	10.403%	$45.6627	$45.66	$45.65	$45.70
Purchase #4	$41.36	9.130%	$45.1362	$45.14	$45.15	$45.10
Purchase #5	$54.27	9.206%	$59.2661	$59.27	$59.25	$59.30
Purchase #6	$44.89	6.664%	$47.8815	$47.88	$47.90	$47.90
Purchase #7	$129.69	4.553%	$135.5948	$135.59	$135.60	$135.60
7 purchase totals =	$792.67		$858.3960	$858.39	$858.40	$858.40