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	$170.64	11.738%	$190.6697	$190.67	$190.65	$190.70
Purchase #2	$32.61	9.807%	$35.8081	$35.81	$35.80	$35.80
Purchase #3	$83.71	3.725%	$86.8282	$86.83	$86.85	$86.80
Purchase #4	$88.86	3.535%	$92.0012	$92.00	$92.00	$92.00
Purchase #5	$161.29	11.306%	$179.5254	$179.53	$179.55	$179.50
Purchase #6	$159.32	8.351%	$172.6248	$172.62	$172.60	$172.60
Purchase #7	$206.97	7.192%	$221.8553	$221.86	$221.85	$221.90
7 purchase totals =	$903.40		$979.3127	$979.32	$979.30	$979.30