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	$137.44	8.556%	$149.1994	$149.20	$149.20	$149.20
Purchase #2	$103.64	6.796%	$110.6834	$110.68	$110.70	$110.70
Purchase #3	$237.69	5.574%	$250.9388	$250.94	$250.95	$250.90
Purchase #4	$109.87	4.496%	$114.8098	$114.81	$114.80	$114.80
Purchase #5	$103.88	7.421%	$111.5889	$111.59	$111.60	$111.60
Purchase #6	$132.59	6.594%	$141.333	$141.33	$141.35	$141.30
Purchase #7	$99.73	4.869%	$104.5859	$104.59	$104.60	$104.60
7 purchase totals =	$924.84		$983.1392	$983.14	$983.20	$983.10