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	$32.68	5.503%	$34.4784	$34.48	$34.50	$34.50
Purchase #2	$98.32	5.150%	$103.3835	$103.38	$103.40	$103.40
Purchase #3	$204.72	3.196%	$211.2629	$211.26	$211.25	$211.30
Purchase #4	$95.32	8.555%	$103.4746	$103.47	$103.45	$103.50
Purchase #5	$78.50	13.674%	$89.2341	$89.23	$89.25	$89.20
Purchase #6	$32.35	12.572%	$36.417	$36.42	$36.40	$36.40
Purchase #7	$208.36	3.858%	$216.3985	$216.40	$216.40	$216.40
7 purchase totals =	$750.25		$794.6490	$794.64	$794.65	$794.70