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	$164.97	12.179%	$185.0617	$185.06	$185.05	$185.10
Purchase #2	$242.42	11.828%	$271.0934	$271.09	$271.10	$271.10
Purchase #3	$30.45	13.334%	$34.5102	$34.51	$34.50	$34.50
Purchase #4	$186.94	13.198%	$211.6123	$211.61	$211.60	$211.60
Purchase #5	$157.41	6.378%	$167.4496	$167.45	$167.45	$167.40
Purchase #6	$42.58	3.771%	$44.1857	$44.19	$44.20	$44.20
Purchase #7	$79.95	11.701%	$89.3049	$89.30	$89.30	$89.30
7 purchase totals =	$904.72		$1,003.2178	$1,003.21	$1,003.20	$1,003.20