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	$99.76	3.676%	$103.4272	$103.43	$103.45	$103.40
Purchase #2	$221.99	11.686%	$247.9318	$247.93	$247.95	$247.90
Purchase #3	$57.35	8.861%	$62.4318	$62.43	$62.45	$62.40
Purchase #4	$143.34	3.340%	$148.1276	$148.13	$148.15	$148.10
Purchase #5	$63.51	11.796%	$71.0016	$71.00	$71.00	$71.00
Purchase #6	$121.92	12.722%	$137.4307	$137.43	$137.45	$137.40
Purchase #7	$46.72	13.549%	$53.0501	$53.05	$53.05	$53.10
7 purchase totals =	$754.59		$823.4008	$823.40	$823.50	$823.30