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	$164.47	12.202%	$184.5386	$184.54	$184.55	$184.50
Purchase #2	$92.33	8.660%	$100.3258	$100.33	$100.35	$100.30
Purchase #3	$232.33	12.355%	$261.0344	$261.03	$261.05	$261.00
Purchase #4	$157.41	5.729%	$166.428	$166.43	$166.45	$166.40
Purchase #5	$72.31	7.311%	$77.5966	$77.60	$77.60	$77.60
Purchase #6	$174.31	6.654%	$185.9086	$185.91	$185.90	$185.90
Purchase #7	$39.78	6.806%	$42.4874	$42.49	$42.50	$42.50
7 purchase totals =	$932.94		$1,018.3194	$1,018.33	$1,018.40	$1,018.20