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	$93.87	5.466%	$99.0009	$99.00	$99.00	$99.00
Purchase #2	$160.77	9.246%	$175.6348	$175.63	$175.65	$175.60
Purchase #3	$39.93	5.548%	$42.1453	$42.15	$42.15	$42.10
Purchase #4	$73.94	11.550%	$82.4801	$82.48	$82.50	$82.50
Purchase #5	$108.57	10.447%	$119.9123	$119.91	$119.90	$119.90
Purchase #6	$218.33	4.760%	$228.7225	$228.72	$228.70	$228.70
Purchase #7	$167.65	7.711%	$180.5775	$180.58	$180.60	$180.60
7 purchase totals =	$863.06		$928.4734	$928.47	$928.50	$928.40