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	$50.69	5.589%	$53.5231	$53.52	$53.50	$53.50
Purchase #2	$242.72	11.517%	$270.6741	$270.67	$270.65	$270.70
Purchase #3	$21.91	13.570%	$24.8832	$24.88	$24.90	$24.90
Purchase #4	$65.76	8.540%	$71.3759	$71.38	$71.40	$71.40
Purchase #5	$18.48	13.243%	$20.9273	$20.93	$20.95	$20.90
Purchase #6	$213.69	12.800%	$241.0423	$241.04	$241.05	$241.00
Purchase #7	$9.73	9.852%	$10.6886	$10.69	$10.70	$10.70
7 purchase totals =	$622.98		$693.1145	$693.11	$693.15	$693.10