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	$30.55	10.392%	$33.7248	$33.72	$33.70	$33.70
Purchase #2	$152.67	6.334%	$162.3401	$162.34	$162.35	$162.30
Purchase #3	$83.73	7.620%	$90.1102	$90.11	$90.10	$90.10
Purchase #4	$6.45	7.418%	$6.9285	$6.93	$6.95	$6.90
Purchase #5	$95.98	9.818%	$105.4033	$105.40	$105.40	$105.40
Purchase #6	$166.68	4.542%	$174.2506	$174.25	$174.25	$174.30
Purchase #7	$97.50	8.328%	$105.6198	$105.62	$105.60	$105.60
7 purchase totals =	$633.56		$678.3773	$678.37	$678.35	$678.30