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	$6.77	5.484%	$7.1413	$7.14	$7.15	$7.10
Purchase #2	$24.94	10.820%	$27.6385	$27.64	$27.65	$27.60
Purchase #3	$42.33	12.269%	$47.5235	$47.52	$47.50	$47.50
Purchase #4	$66.38	12.490%	$74.6709	$74.67	$74.65	$74.70
Purchase #5	$72.52	8.784%	$78.8902	$78.89	$78.90	$78.90
Purchase #6	$200.57	4.808%	$210.2134	$210.21	$210.20	$210.20
Purchase #7	$28.81	5.419%	$30.3712	$30.37	$30.35	$30.40
7 purchase totals =	$442.32		$476.4490	$476.44	$476.40	$476.40