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	$188.77	13.248%	$213.7782	$213.78	$213.80	$213.80
Purchase #2	$95.67	4.337%	$99.8192	$99.82	$99.80	$99.80
Purchase #3	$209.77	10.586%	$231.9763	$231.98	$232.00	$232.00
Purchase #4	$46.28	10.234%	$51.0163	$51.02	$51.00	$51.00
Purchase #5	$89.58	11.585%	$99.9578	$99.96	$99.95	$100.00
Purchase #6	$204.50	12.762%	$230.5983	$230.60	$230.60	$230.60
Purchase #7	$162.61	5.616%	$171.7422	$171.74	$171.75	$171.70
7 purchase totals =	$997.18		$1,098.8883	$1,098.90	$1,098.90	$1,098.90