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	$33.88	3.179%	$34.957	$34.96	$34.95	$35.00
Purchase #2	$123.39	9.262%	$134.8184	$134.82	$134.80	$134.80
Purchase #3	$62.33	13.653%	$70.8399	$70.84	$70.85	$70.80
Purchase #4	$70.36	11.404%	$78.3839	$78.38	$78.40	$78.40
Purchase #5	$238.34	9.449%	$260.8607	$260.86	$260.85	$260.90
Purchase #6	$56.96	5.310%	$59.9846	$59.98	$60.00	$60.00
Purchase #7	$36.68	7.657%	$39.4886	$39.49	$39.50	$39.50
7 purchase totals =	$621.94		$679.3331	$679.33	$679.35	$679.40