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	$79.92	6.729%	$85.2978	$85.30	$85.30	$85.30
Purchase #2	$33.96	3.364%	$35.1024	$35.10	$35.10	$35.10
Purchase #3	$243.61	13.286%	$275.976	$275.98	$276.00	$276.00
Purchase #4	$29.58	12.867%	$33.3861	$33.39	$33.40	$33.40
Purchase #5	$54.46	7.791%	$58.703	$58.70	$58.70	$58.70
Purchase #6	$123.41	7.132%	$132.2116	$132.21	$132.20	$132.20
Purchase #7	$130.47	7.210%	$139.8769	$139.88	$139.90	$139.90
7 purchase totals =	$695.41		$760.5538	$760.56	$760.60	$760.60