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	$87.40	13.498%	$99.1973	$99.20	$99.20	$99.20
Purchase #2	$204.65	12.434%	$230.0962	$230.10	$230.10	$230.10
Purchase #3	$182.45	7.637%	$196.3837	$196.38	$196.40	$196.40
Purchase #4	$217.57	7.334%	$233.5266	$233.53	$233.55	$233.50
Purchase #5	$44.40	12.623%	$50.0046	$50.00	$50.00	$50.00
Purchase #6	$130.56	12.193%	$146.4792	$146.48	$146.50	$146.50
Purchase #7	$189.40	3.410%	$195.8585	$195.86	$195.85	$195.90
7 purchase totals =	$1,056.43		$1,151.5461	$1,151.55	$1,151.60	$1,151.60