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	$68.33	6.103%	$72.5002	$72.50	$72.50	$72.50
Purchase #2	$101.33	8.158%	$109.5965	$109.60	$109.60	$109.60
Purchase #3	$199.77	4.397%	$208.5539	$208.55	$208.55	$208.60
Purchase #4	$72.91	8.132%	$78.839	$78.84	$78.85	$78.80
Purchase #5	$209.56	13.294%	$237.4189	$237.42	$237.40	$237.40
Purchase #6	$106.60	7.392%	$114.4799	$114.48	$114.50	$114.50
Purchase #7	$32.46	10.715%	$35.9381	$35.94	$35.95	$35.90
7 purchase totals =	$790.96		$857.3265	$857.33	$857.35	$857.30