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	$172.65	4.175%	$179.8581	$179.86	$179.85	$179.90
Purchase #2	$34.69	12.833%	$39.1418	$39.14	$39.15	$39.10
Purchase #3	$161.85	12.821%	$182.6008	$182.60	$182.60	$182.60
Purchase #4	$48.76	12.266%	$54.7409	$54.74	$54.75	$54.70
Purchase #5	$116.32	3.362%	$120.2307	$120.23	$120.25	$120.20
Purchase #6	$40.72	10.227%	$44.8844	$44.88	$44.90	$44.90
Purchase #7	$112.87	10.315%	$124.5125	$124.51	$124.50	$124.50
7 purchase totals =	$687.86		$745.9692	$745.96	$746.00	$745.90