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	$138.57	8.619%	$150.5133	$150.51	$150.50	$150.50
Purchase #2	$24.74	11.205%	$27.5121	$27.51	$27.50	$27.50
Purchase #3	$214.77	4.240%	$223.8762	$223.88	$223.90	$223.90
Purchase #4	$20.69	12.671%	$23.3116	$23.31	$23.30	$23.30
Purchase #5	$35.48	7.776%	$38.2389	$38.24	$38.25	$38.20
Purchase #6	$189.51	11.621%	$211.533	$211.53	$211.55	$211.50
Purchase #7	$71.90	6.250%	$76.3938	$76.39	$76.40	$76.40
7 purchase totals =	$695.66		$751.3789	$751.37	$751.40	$751.30