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	$37.64	11.276%	$41.8843	$41.88	$41.90	$41.90
Purchase #2	$171.30	13.550%	$194.5112	$194.51	$194.50	$194.50
Purchase #3	$192.26	12.365%	$216.0329	$216.03	$216.05	$216.00
Purchase #4	$63.96	3.438%	$66.1589	$66.16	$66.15	$66.20
Purchase #5	$50.92	13.614%	$57.8522	$57.85	$57.85	$57.90
Purchase #6	$180.81	5.649%	$191.024	$191.02	$191.00	$191.00
Purchase #7	$50.82	13.105%	$57.48	$57.48	$57.50	$57.50
7 purchase totals =	$747.71		$824.9435	$824.93	$824.95	$825.00