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	$165.34	12.152%	$185.4321	$185.43	$185.45	$185.40
Purchase #2	$50.32	9.489%	$55.0949	$55.09	$55.10	$55.10
Purchase #3	$234.43	12.746%	$264.3104	$264.31	$264.30	$264.30
Purchase #4	$190.81	7.193%	$204.535	$204.54	$204.55	$204.50
Purchase #5	$144.70	11.571%	$161.4432	$161.44	$161.45	$161.40
Purchase #6	$208.93	3.571%	$216.3909	$216.39	$216.40	$216.40
Purchase #7	$82.60	11.308%	$91.9404	$91.94	$91.95	$91.90
7 purchase totals =	$1,077.13		$1,179.1469	$1,179.14	$1,179.20	$1,179.00