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	$35.71	8.756%	$38.8368	$38.84	$38.85	$38.80
Purchase #2	$160.95	8.703%	$174.9575	$174.96	$174.95	$175.00
Purchase #3	$17.94	3.751%	$18.6129	$18.61	$18.60	$18.60
Purchase #4	$47.53	4.600%	$49.7164	$49.72	$49.70	$49.70
Purchase #5	$80.72	6.445%	$85.9224	$85.92	$85.90	$85.90
Purchase #6	$164.42	12.655%	$185.2274	$185.23	$185.25	$185.20
Purchase #7	$86.32	3.221%	$89.1004	$89.10	$89.10	$89.10
7 purchase totals =	$593.59		$642.3738	$642.38	$642.35	$642.30