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	$124.71	8.769%	$135.6458	$135.65	$135.65	$135.60
Purchase #2	$179.59	7.126%	$192.3876	$192.39	$192.40	$192.40
Purchase #3	$239.42	6.818%	$255.7437	$255.74	$255.75	$255.70
Purchase #4	$86.58	4.499%	$90.4752	$90.48	$90.50	$90.50
Purchase #5	$18.70	11.353%	$20.823	$20.82	$20.80	$20.80
Purchase #6	$229.58	11.288%	$255.495	$255.50	$255.50	$255.50
Purchase #7	$29.31	4.498%	$30.6284	$30.63	$30.65	$30.60
7 purchase totals =	$907.89		$981.1987	$981.21	$981.25	$981.10