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	$52.61	5.467%	$55.4862	$55.49	$55.50	$55.50
Purchase #2	$234.71	8.293%	$254.1745	$254.17	$254.15	$254.20
Purchase #3	$127.89	4.653%	$133.8407	$133.84	$133.85	$133.80
Purchase #4	$107.38	11.171%	$119.3754	$119.38	$119.40	$119.40
Purchase #5	$136.73	11.551%	$152.5237	$152.52	$152.50	$152.50
Purchase #6	$76.78	7.760%	$82.7381	$82.74	$82.75	$82.70
Purchase #7	$207.49	8.806%	$225.7616	$225.76	$225.75	$225.80
7 purchase totals =	$943.59		$1,023.9002	$1,023.90	$1,023.90	$1,023.90