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	$127.46	13.385%	$144.5205	$144.52	$144.50	$144.50
Purchase #2	$242.43	5.270%	$255.2061	$255.21	$255.20	$255.20
Purchase #3	$105.38	13.328%	$119.425	$119.43	$119.45	$119.40
Purchase #4	$20.29	10.794%	$22.4801	$22.48	$22.50	$22.50
Purchase #5	$65.37	7.799%	$70.4682	$70.47	$70.45	$70.50
Purchase #6	$138.33	10.691%	$153.1189	$153.12	$153.10	$153.10
Purchase #7	$25.30	4.846%	$26.526	$26.53	$26.55	$26.50
7 purchase totals =	$724.56		$791.7448	$791.76	$791.75	$791.70