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	$75.91	7.838%	$81.8598	$81.86	$81.85	$81.90
Purchase #2	$140.74	13.476%	$159.7061	$159.71	$159.70	$159.70
Purchase #3	$98.31	6.854%	$105.0482	$105.05	$105.05	$105.00
Purchase #4	$24.83	3.368%	$25.6663	$25.67	$25.65	$25.70
Purchase #5	$53.36	11.751%	$59.6303	$59.63	$59.65	$59.60
Purchase #6	$102.63	11.805%	$114.7455	$114.75	$114.75	$114.70
Purchase #7	$83.93	6.679%	$89.5357	$89.54	$89.55	$89.50
7 purchase totals =	$579.71		$636.1919	$636.21	$636.20	$636.10