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	$23.92	6.412%	$25.4538	$25.45	$25.45	$25.50
Purchase #2	$209.33	8.178%	$226.449	$226.45	$226.45	$226.40
Purchase #3	$137.89	6.215%	$146.4599	$146.46	$146.45	$146.50
Purchase #4	$250.60	13.843%	$285.2906	$285.29	$285.30	$285.30
Purchase #5	$50.93	6.844%	$54.4156	$54.42	$54.40	$54.40
Purchase #6	$41.54	8.337%	$45.0032	$45.00	$45.00	$45.00
Purchase #7	$86.46	12.578%	$97.3349	$97.33	$97.35	$97.30
7 purchase totals =	$800.67		$880.4070	$880.40	$880.40	$880.40