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	$220.71	6.352%	$234.7295	$234.73	$234.75	$234.70
Purchase #2	$243.46	11.362%	$271.1219	$271.12	$271.10	$271.10
Purchase #3	$54.55	9.787%	$59.8888	$59.89	$59.90	$59.90
Purchase #4	$25.67	9.295%	$28.056	$28.06	$28.05	$28.10
Purchase #5	$124.41	12.129%	$139.4997	$139.50	$139.50	$139.50
Purchase #6	$85.75	11.528%	$95.6353	$95.64	$95.65	$95.60
Purchase #7	$158.90	5.406%	$167.4901	$167.49	$167.50	$167.50
7 purchase totals =	$913.45		$996.4213	$996.43	$996.45	$996.40