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	$11.28	11.194%	$12.5427	$12.54	$12.55	$12.50
Purchase #2	$212.75	5.234%	$223.8853	$223.89	$223.90	$223.90
Purchase #3	$108.50	7.801%	$116.9641	$116.96	$116.95	$117.00
Purchase #4	$221.44	7.865%	$238.8563	$238.86	$238.85	$238.90
Purchase #5	$6.78	13.640%	$7.7048	$7.70	$7.70	$7.70
Purchase #6	$138.66	10.374%	$153.0446	$153.04	$153.05	$153.00
Purchase #7	$150.89	3.678%	$156.4397	$156.44	$156.45	$156.40
7 purchase totals =	$850.30		$909.4375	$909.43	$909.45	$909.40