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	$90.85	6.534%	$96.7861	$96.79	$96.80	$96.80
Purchase #2	$68.75	4.394%	$71.7709	$71.77	$71.75	$71.80
Purchase #3	$15.56	3.403%	$16.0895	$16.09	$16.10	$16.10
Purchase #4	$183.91	11.187%	$204.484	$204.48	$204.50	$204.50
Purchase #5	$181.78	3.508%	$188.1568	$188.16	$188.15	$188.20
Purchase #6	$40.29	6.321%	$42.8367	$42.84	$42.85	$42.80
Purchase #7	$44.75	4.667%	$46.8385	$46.84	$46.85	$46.80
7 purchase totals =	$625.89		$666.9625	$666.97	$667.00	$667.00