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	$52.43	9.449%	$57.3841	$57.38	$57.40	$57.40
Purchase #2	$26.72	4.817%	$28.0071	$28.01	$28.00	$28.00
Purchase #3	$43.96	8.627%	$47.7524	$47.75	$47.75	$47.80
Purchase #4	$52.37	6.614%	$55.8338	$55.83	$55.85	$55.80
Purchase #5	$47.37	12.445%	$53.2652	$53.27	$53.25	$53.30
Purchase #6	$211.53	12.667%	$238.3245	$238.32	$238.30	$238.30
Purchase #7	$234.34	9.142%	$255.7634	$255.76	$255.75	$255.80
7 purchase totals =	$668.72		$736.3305	$736.32	$736.30	$736.40