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	$120.56	10.563%	$133.2948	$133.29	$133.30	$133.30
Purchase #2	$161.69	5.220%	$170.1302	$170.13	$170.15	$170.10
Purchase #3	$147.73	3.214%	$152.478	$152.48	$152.50	$152.50
Purchase #4	$191.61	11.829%	$214.2755	$214.28	$214.30	$214.30
Purchase #5	$35.86	3.636%	$37.1639	$37.16	$37.15	$37.20
Purchase #6	$32.92	7.744%	$35.4693	$35.47	$35.45	$35.50
Purchase #7	$63.40	13.273%	$71.8151	$71.82	$71.80	$71.80
7 purchase totals =	$753.77		$814.6268	$814.63	$814.65	$814.70