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	$75.43	9.139%	$82.3235	$82.32	$82.30	$82.30
Purchase #2	$143.31	5.277%	$150.8725	$150.87	$150.85	$150.90
Purchase #3	$35.63	13.151%	$40.3157	$40.32	$40.30	$40.30
Purchase #4	$128.48	3.128%	$132.4989	$132.50	$132.50	$132.50
Purchase #5	$189.54	10.280%	$209.0247	$209.02	$209.00	$209.00
Purchase #6	$69.63	10.823%	$77.1661	$77.17	$77.15	$77.20
Purchase #7	$159.27	4.839%	$166.9771	$166.98	$167.00	$167.00
7 purchase totals =	$801.29		$859.1785	$859.18	$859.10	$859.20