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	$5.63	4.572%	$5.8874	$5.89	$5.90	$5.90
Purchase #2	$178.85	6.317%	$190.148	$190.15	$190.15	$190.10
Purchase #3	$165.83	11.610%	$185.0829	$185.08	$185.10	$185.10
Purchase #4	$116.83	5.439%	$123.1844	$123.18	$123.20	$123.20
Purchase #5	$116.79	13.310%	$132.3347	$132.33	$132.35	$132.30
Purchase #6	$176.49	6.118%	$187.2877	$187.29	$187.30	$187.30
Purchase #7	$83.76	8.598%	$90.9617	$90.96	$90.95	$91.00
7 purchase totals =	$844.18		$914.8868	$914.88	$914.95	$914.90