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	$150.63	9.754%	$165.3225	$165.32	$165.30	$165.30
Purchase #2	$87.38	4.672%	$91.4624	$91.46	$91.45	$91.50
Purchase #3	$135.45	10.395%	$149.53	$149.53	$149.55	$149.50
Purchase #4	$127.39	13.516%	$144.608	$144.61	$144.60	$144.60
Purchase #5	$139.80	4.690%	$146.3566	$146.36	$146.35	$146.40
Purchase #6	$14.87	7.178%	$15.9374	$15.94	$15.95	$15.90
Purchase #7	$126.39	4.352%	$131.8905	$131.89	$131.90	$131.90
7 purchase totals =	$781.91		$845.1074	$845.11	$845.10	$845.10