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	$31.89	10.454%	$35.2238	$35.22	$35.20	$35.20
Purchase #2	$141.71	12.609%	$159.5782	$159.58	$159.60	$159.60
Purchase #3	$150.99	13.856%	$171.9112	$171.91	$171.90	$171.90
Purchase #4	$138.34	3.781%	$143.5706	$143.57	$143.55	$143.60
Purchase #5	$45.33	10.667%	$50.1654	$50.17	$50.15	$50.20
Purchase #6	$85.34	4.617%	$89.2801	$89.28	$89.30	$89.30
Purchase #7	$159.27	7.707%	$171.5449	$171.54	$171.55	$171.50
7 purchase totals =	$752.87		$821.2742	$821.27	$821.25	$821.30