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	$29.46	3.462%	$30.4799	$30.48	$30.50	$30.50
Purchase #2	$18.59	9.347%	$20.3276	$20.33	$20.35	$20.30
Purchase #3	$98.55	10.783%	$109.1766	$109.18	$109.20	$109.20
Purchase #4	$187.93	5.417%	$198.1102	$198.11	$198.10	$198.10
Purchase #5	$54.66	12.499%	$61.492	$61.49	$61.50	$61.50
Purchase #6	$35.85	8.338%	$38.8392	$38.84	$38.85	$38.80
Purchase #7	$183.62	11.707%	$205.1164	$205.12	$205.10	$205.10
7 purchase totals =	$608.66		$663.5419	$663.55	$663.60	$663.50