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	$140.28	13.657%	$159.438	$159.44	$159.45	$159.40
Purchase #2	$190.82	10.290%	$210.4554	$210.46	$210.45	$210.50
Purchase #3	$48.69	6.333%	$51.7735	$51.77	$51.75	$51.80
Purchase #4	$57.58	3.165%	$59.4024	$59.40	$59.40	$59.40
Purchase #5	$157.52	10.691%	$174.3605	$174.36	$174.35	$174.40
Purchase #6	$33.58	10.611%	$37.1432	$37.14	$37.15	$37.10
Purchase #7	$86.72	11.794%	$96.9478	$96.95	$96.95	$96.90
7 purchase totals =	$715.19		$789.5208	$789.52	$789.50	$789.50