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	$165.87	3.758%	$172.1034	$172.10	$172.10	$172.10
Purchase #2	$200.94	5.810%	$212.6146	$212.61	$212.60	$212.60
Purchase #3	$37.43	11.156%	$41.6057	$41.61	$41.60	$41.60
Purchase #4	$172.83	10.820%	$191.5302	$191.53	$191.55	$191.50
Purchase #5	$237.61	11.296%	$264.4504	$264.45	$264.45	$264.50
Purchase #6	$6.66	12.732%	$7.508	$7.51	$7.50	$7.50
Purchase #7	$31.97	9.663%	$35.0593	$35.06	$35.05	$35.10
7 purchase totals =	$853.31		$924.8716	$924.87	$924.85	$924.90