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	$20.29	6.137%	$21.5352	$21.54	$21.55	$21.50
Purchase #2	$28.56	12.497%	$32.1291	$32.13	$32.15	$32.10
Purchase #3	$13.72	13.204%	$15.5316	$15.53	$15.55	$15.50
Purchase #4	$194.32	3.695%	$201.5001	$201.50	$201.50	$201.50
Purchase #5	$37.62	13.397%	$42.66	$42.66	$42.65	$42.70
Purchase #6	$248.77	10.298%	$274.3883	$274.39	$274.40	$274.40
Purchase #7	$91.33	12.589%	$102.8275	$102.83	$102.85	$102.80
7 purchase totals =	$634.61		$690.5718	$690.58	$690.65	$690.50