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	$78.93	12.777%	$89.0149	$89.01	$89.00	$89.00
Purchase #2	$65.63	12.828%	$74.049	$74.05	$74.05	$74.00
Purchase #3	$92.60	9.600%	$101.4896	$101.49	$101.50	$101.50
Purchase #4	$34.27	13.107%	$38.7618	$38.76	$38.75	$38.80
Purchase #5	$183.86	13.863%	$209.3485	$209.35	$209.35	$209.30
Purchase #6	$98.83	7.158%	$105.9043	$105.90	$105.90	$105.90
Purchase #7	$180.54	13.503%	$204.9183	$204.92	$204.90	$204.90
7 purchase totals =	$734.66		$823.4864	$823.48	$823.45	$823.40