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	$39.68	9.703%	$43.5302	$43.53	$43.55	$43.50
Purchase #2	$33.38	12.538%	$37.5652	$37.57	$37.55	$37.60
Purchase #3	$218.68	9.182%	$238.7592	$238.76	$238.75	$238.80
Purchase #4	$234.52	4.842%	$245.8755	$245.88	$245.90	$245.90
Purchase #5	$86.79	3.325%	$89.6758	$89.68	$89.70	$89.70
Purchase #6	$47.86	9.830%	$52.5646	$52.56	$52.55	$52.60
Purchase #7	$170.48	7.504%	$183.2728	$183.27	$183.25	$183.30
7 purchase totals =	$831.39		$891.2433	$891.25	$891.25	$891.40