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	$212.59	13.789%	$241.904	$241.90	$241.90	$241.90
Purchase #2	$190.51	6.476%	$202.8474	$202.85	$202.85	$202.80
Purchase #3	$93.63	6.710%	$99.9126	$99.91	$99.90	$99.90
Purchase #4	$215.46	12.443%	$242.2697	$242.27	$242.25	$242.30
Purchase #5	$27.30	5.358%	$28.7627	$28.76	$28.75	$28.80
Purchase #6	$94.73	4.379%	$98.8782	$98.88	$98.90	$98.90
Purchase #7	$158.45	10.669%	$175.355	$175.36	$175.35	$175.40
7 purchase totals =	$992.67		$1,089.9296	$1,089.93	$1,089.90	$1,090.00