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	$85.86	5.285%	$90.3977	$90.40	$90.40	$90.40
Purchase #2	$83.91	5.573%	$88.5863	$88.59	$88.60	$88.60
Purchase #3	$27.94	3.415%	$28.8942	$28.89	$28.90	$28.90
Purchase #4	$120.60	9.770%	$132.3826	$132.38	$132.40	$132.40
Purchase #5	$228.37	7.204%	$244.8218	$244.82	$244.80	$244.80
Purchase #6	$131.67	6.142%	$139.7572	$139.76	$139.75	$139.80
Purchase #7	$237.81	7.824%	$256.4163	$256.42	$256.40	$256.40
7 purchase totals =	$916.16		$981.2561	$981.26	$981.25	$981.30