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	$31.38	12.435%	$35.2821	$35.28	$35.30	$35.30
Purchase #2	$79.60	12.335%	$89.4187	$89.42	$89.40	$89.40
Purchase #3	$131.67	6.199%	$139.8322	$139.83	$139.85	$139.80
Purchase #4	$79.81	10.484%	$88.1773	$88.18	$88.20	$88.20
Purchase #5	$26.71	11.276%	$29.7218	$29.72	$29.70	$29.70
Purchase #6	$94.53	6.323%	$100.5071	$100.51	$100.50	$100.50
Purchase #7	$109.48	9.514%	$119.8959	$119.90	$119.90	$119.90
7 purchase totals =	$553.18		$602.8351	$602.84	$602.85	$602.80