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	$158.30	6.598%	$168.7446	$168.74	$168.75	$168.70
Purchase #2	$171.94	13.771%	$195.6179	$195.62	$195.60	$195.60
Purchase #3	$75.90	3.319%	$78.4191	$78.42	$78.40	$78.40
Purchase #4	$152.73	10.475%	$168.7285	$168.73	$168.75	$168.70
Purchase #5	$107.42	7.155%	$115.1059	$115.11	$115.10	$115.10
Purchase #6	$32.51	9.302%	$35.5341	$35.53	$35.55	$35.50
Purchase #7	$81.98	4.770%	$85.8904	$85.89	$85.90	$85.90
7 purchase totals =	$780.78		$848.0405	$848.04	$848.05	$847.90