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	$155.69	12.713%	$175.4829	$175.48	$175.50	$175.50
Purchase #2	$147.50	9.409%	$161.3783	$161.38	$161.40	$161.40
Purchase #3	$154.29	13.205%	$174.664	$174.66	$174.65	$174.70
Purchase #4	$164.81	13.164%	$186.5056	$186.51	$186.50	$186.50
Purchase #5	$87.73	3.397%	$90.7102	$90.71	$90.70	$90.70
Purchase #6	$119.98	11.772%	$134.104	$134.10	$134.10	$134.10
Purchase #7	$245.89	7.366%	$264.0023	$264.00	$264.00	$264.00
7 purchase totals =	$1,075.89		$1,186.8473	$1,186.84	$1,186.85	$1,186.90