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	$33.96	3.711%	$35.2203	$35.22	$35.20	$35.20
Purchase #2	$85.41	4.182%	$88.9818	$88.98	$89.00	$89.00
Purchase #3	$128.43	8.833%	$139.7742	$139.77	$139.75	$139.80
Purchase #4	$75.47	4.687%	$79.0073	$79.01	$79.00	$79.00
Purchase #5	$52.89	4.502%	$55.2711	$55.27	$55.25	$55.30
Purchase #6	$57.32	9.677%	$62.8669	$62.87	$62.85	$62.90
Purchase #7	$73.55	9.665%	$80.6586	$80.66	$80.65	$80.70
7 purchase totals =	$507.03		$541.7802	$541.78	$541.70	$541.90