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	$23.56	5.385%	$24.8287	$24.83	$24.85	$24.80
Purchase #2	$52.53	4.787%	$55.0446	$55.04	$55.05	$55.00
Purchase #3	$217.52	6.424%	$231.4935	$231.49	$231.50	$231.50
Purchase #4	$109.61	13.384%	$124.2802	$124.28	$124.30	$124.30
Purchase #5	$45.73	9.327%	$49.9952	$50.00	$50.00	$50.00
Purchase #6	$171.95	12.688%	$193.767	$193.77	$193.75	$193.80
Purchase #7	$27.89	11.686%	$31.1492	$31.15	$31.15	$31.10
7 purchase totals =	$648.79		$710.5584	$710.56	$710.60	$710.50