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	$250.42	5.781%	$264.8968	$264.90	$264.90	$264.90
Purchase #2	$116.35	10.669%	$128.7634	$128.76	$128.75	$128.80
Purchase #3	$127.76	9.667%	$140.1106	$140.11	$140.10	$140.10
Purchase #4	$53.72	9.389%	$58.7638	$58.76	$58.75	$58.80
Purchase #5	$219.31	13.794%	$249.5616	$249.56	$249.55	$249.60
Purchase #6	$237.87	6.553%	$253.4576	$253.46	$253.45	$253.50
Purchase #7	$54.72	8.708%	$59.485	$59.49	$59.50	$59.50
7 purchase totals =	$1,060.15		$1,155.0388	$1,155.04	$1,155.00	$1,155.20