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	$222.81	6.540%	$237.3818	$237.38	$237.40	$237.40
Purchase #2	$52.73	12.599%	$59.3735	$59.37	$59.35	$59.40
Purchase #3	$118.52	3.516%	$122.6872	$122.69	$122.70	$122.70
Purchase #4	$62.33	12.107%	$69.8763	$69.88	$69.90	$69.90
Purchase #5	$86.34	3.652%	$89.4931	$89.49	$89.50	$89.50
Purchase #6	$211.38	4.155%	$220.1628	$220.16	$220.15	$220.20
Purchase #7	$115.46	13.536%	$131.0887	$131.09	$131.10	$131.10
7 purchase totals =	$869.57		$930.0634	$930.06	$930.10	$930.20