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	$5.83	8.401%	$6.3198	$6.32	$6.30	$6.30
Purchase #2	$210.27	12.576%	$236.7136	$236.71	$236.70	$236.70
Purchase #3	$126.29	13.441%	$143.2646	$143.26	$143.25	$143.30
Purchase #4	$71.73	3.873%	$74.5081	$74.51	$74.50	$74.50
Purchase #5	$86.31	3.694%	$89.4983	$89.50	$89.50	$89.50
Purchase #6	$26.27	4.623%	$27.4845	$27.48	$27.50	$27.50
Purchase #7	$112.56	4.676%	$117.8233	$117.82	$117.80	$117.80
7 purchase totals =	$639.26		$695.6122	$695.60	$695.55	$695.60