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	$246.29	13.451%	$279.4185	$279.42	$279.40	$279.40
Purchase #2	$74.81	7.494%	$80.4163	$80.42	$80.40	$80.40
Purchase #3	$27.74	6.257%	$29.4757	$29.48	$29.50	$29.50
Purchase #4	$56.46	4.604%	$59.0594	$59.06	$59.05	$59.10
Purchase #5	$195.78	4.821%	$205.2186	$205.22	$205.20	$205.20
Purchase #6	$250.53	8.472%	$271.7549	$271.75	$271.75	$271.80
Purchase #7	$72.90	8.384%	$79.0119	$79.01	$79.00	$79.00
7 purchase totals =	$924.51		$1,004.3553	$1,004.36	$1,004.30	$1,004.40