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	$128.34	3.111%	$132.3327	$132.33	$132.35	$132.30
Purchase #2	$100.77	10.224%	$111.0727	$111.07	$111.05	$111.10
Purchase #3	$26.65	7.614%	$28.6791	$28.68	$28.70	$28.70
Purchase #4	$57.40	4.342%	$59.8923	$59.89	$59.90	$59.90
Purchase #5	$232.31	8.380%	$251.7776	$251.78	$251.80	$251.80
Purchase #6	$167.88	7.684%	$180.7799	$180.78	$180.80	$180.80
Purchase #7	$208.81	7.827%	$225.1536	$225.15	$225.15	$225.20
7 purchase totals =	$922.16		$989.6879	$989.68	$989.75	$989.80