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	$31.51	11.768%	$35.2181	$35.22	$35.20	$35.20
Purchase #2	$207.82	11.448%	$231.6112	$231.61	$231.60	$231.60
Purchase #3	$72.91	13.820%	$82.9862	$82.99	$83.00	$83.00
Purchase #4	$58.92	4.525%	$61.5861	$61.59	$61.60	$61.60
Purchase #5	$159.78	11.504%	$178.1611	$178.16	$178.15	$178.20
Purchase #6	$178.66	11.350%	$198.9379	$198.94	$198.95	$198.90
Purchase #7	$144.81	4.154%	$150.8254	$150.83	$150.85	$150.80
7 purchase totals =	$854.41		$939.3260	$939.34	$939.35	$939.30