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	$242.89	6.401%	$258.4374	$258.44	$258.45	$258.40
Purchase #2	$123.79	4.594%	$129.4769	$129.48	$129.50	$129.50
Purchase #3	$62.32	10.813%	$69.0587	$69.06	$69.05	$69.10
Purchase #4	$83.94	9.872%	$92.2266	$92.23	$92.25	$92.20
Purchase #5	$96.49	4.593%	$100.9218	$100.92	$100.90	$100.90
Purchase #6	$76.27	8.202%	$82.5257	$82.53	$82.55	$82.50
Purchase #7	$27.69	11.505%	$30.8757	$30.88	$30.90	$30.90
7 purchase totals =	$713.39		$763.5228	$763.54	$763.60	$763.50