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	$45.78	3.825%	$47.5311	$47.53	$47.55	$47.50
Purchase #2	$139.36	5.213%	$146.6248	$146.62	$146.60	$146.60
Purchase #3	$89.78	11.846%	$100.4153	$100.42	$100.40	$100.40
Purchase #4	$165.82	3.261%	$171.2274	$171.23	$171.25	$171.20
Purchase #5	$15.54	8.196%	$16.8137	$16.81	$16.80	$16.80
Purchase #6	$18.94	8.673%	$20.5827	$20.58	$20.60	$20.60
Purchase #7	$104.96	7.424%	$112.7522	$112.75	$112.75	$112.80
7 purchase totals =	$580.18		$615.9472	$615.94	$615.95	$615.90