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	$41.76	9.216%	$45.6086	$45.61	$45.60	$45.60
Purchase #2	$154.65	12.813%	$174.4653	$174.47	$174.45	$174.50
Purchase #3	$31.58	5.499%	$33.3166	$33.32	$33.30	$33.30
Purchase #4	$33.81	13.470%	$38.3642	$38.36	$38.35	$38.40
Purchase #5	$161.48	9.289%	$176.4799	$176.48	$176.50	$176.50
Purchase #6	$63.31	10.293%	$69.8265	$69.83	$69.85	$69.80
Purchase #7	$161.86	13.585%	$183.8487	$183.85	$183.85	$183.80
7 purchase totals =	$648.45		$721.9098	$721.92	$721.90	$721.90