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	$64.38	3.285%	$66.4949	$66.49	$66.50	$66.50
Purchase #2	$146.93	13.778%	$167.174	$167.17	$167.15	$167.20
Purchase #3	$211.99	8.419%	$229.8374	$229.84	$229.85	$229.80
Purchase #4	$174.32	12.186%	$195.5626	$195.56	$195.55	$195.60
Purchase #5	$35.41	5.705%	$37.4301	$37.43	$37.45	$37.40
Purchase #6	$200.63	5.413%	$211.4901	$211.49	$211.50	$211.50
Purchase #7	$35.56	6.535%	$37.8838	$37.88	$37.90	$37.90
7 purchase totals =	$869.22		$945.8729	$945.86	$945.90	$945.90