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	$52.43	4.435%	$54.7553	$54.76	$54.75	$54.80
Purchase #2	$92.83	5.766%	$98.1826	$98.18	$98.20	$98.20
Purchase #3	$207.67	8.747%	$225.8349	$225.83	$225.85	$225.80
Purchase #4	$47.66	13.394%	$54.0436	$54.04	$54.05	$54.00
Purchase #5	$66.79	13.541%	$75.834	$75.83	$75.85	$75.80
Purchase #6	$18.80	8.228%	$20.3469	$20.35	$20.35	$20.30
Purchase #7	$55.32	11.822%	$61.8599	$61.86	$61.85	$61.90
7 purchase totals =	$541.50		$590.8572	$590.85	$590.90	$590.80