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	$19.29	6.321%	$20.5093	$20.51	$20.50	$20.50
Purchase #2	$243.36	3.291%	$251.369	$251.37	$251.35	$251.40
Purchase #3	$177.30	6.618%	$189.0337	$189.03	$189.05	$189.00
Purchase #4	$109.55	12.642%	$123.3993	$123.40	$123.40	$123.40
Purchase #5	$147.72	3.828%	$153.3747	$153.37	$153.35	$153.40
Purchase #6	$40.52	12.453%	$45.566	$45.57	$45.55	$45.60
Purchase #7	$165.73	3.547%	$171.6084	$171.61	$171.60	$171.60
7 purchase totals =	$903.47		$954.8604	$954.86	$954.80	$954.90