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	$31.49	13.590%	$35.7695	$35.77	$35.75	$35.80
Purchase #2	$166.57	13.376%	$188.8504	$188.85	$188.85	$188.90
Purchase #3	$180.66	8.722%	$196.4172	$196.42	$196.40	$196.40
Purchase #4	$165.36	13.528%	$187.7299	$187.73	$187.75	$187.70
Purchase #5	$37.52	8.498%	$40.7084	$40.71	$40.70	$40.70
Purchase #6	$241.47	5.579%	$254.9416	$254.94	$254.95	$254.90
Purchase #7	$83.44	4.234%	$86.9728	$86.97	$86.95	$87.00
7 purchase totals =	$906.51		$991.3898	$991.39	$991.35	$991.40