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	$125.51	13.858%	$142.9032	$142.90	$142.90	$142.90
Purchase #2	$178.89	6.464%	$190.4534	$190.45	$190.45	$190.50
Purchase #3	$16.89	11.869%	$18.8947	$18.89	$18.90	$18.90
Purchase #4	$107.96	5.659%	$114.0695	$114.07	$114.05	$114.10
Purchase #5	$44.59	11.199%	$49.5836	$49.58	$49.60	$49.60
Purchase #6	$111.61	8.173%	$120.7319	$120.73	$120.75	$120.70
Purchase #7	$211.38	4.391%	$220.6617	$220.66	$220.65	$220.70
7 purchase totals =	$796.83		$857.2980	$857.28	$857.30	$857.40