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	$25.93	3.278%	$26.78	$26.78	$26.80	$26.80
Purchase #2	$116.48	4.184%	$121.3535	$121.35	$121.35	$121.40
Purchase #3	$148.77	11.427%	$165.7699	$165.77	$165.75	$165.80
Purchase #4	$80.46	11.578%	$89.7757	$89.78	$89.80	$89.80
Purchase #5	$96.57	6.512%	$102.8586	$102.86	$102.85	$102.90
Purchase #6	$107.75	3.361%	$111.3715	$111.37	$111.35	$111.40
Purchase #7	$115.47	13.528%	$131.0908	$131.09	$131.10	$131.10
7 purchase totals =	$691.43		$749.0000	$749.00	$749.00	$749.20