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	$54.34	5.818%	$57.5015	$57.50	$57.50	$57.50
Purchase #2	$144.69	4.529%	$151.243	$151.24	$151.25	$151.20
Purchase #3	$141.97	4.816%	$148.8073	$148.81	$148.80	$148.80
Purchase #4	$104.60	7.181%	$112.1113	$112.11	$112.10	$112.10
Purchase #5	$221.89	6.421%	$236.1376	$236.14	$236.15	$236.10
Purchase #6	$77.49	10.429%	$85.5714	$85.57	$85.55	$85.60
Purchase #7	$18.66	11.393%	$20.7859	$20.79	$20.80	$20.80
7 purchase totals =	$763.64		$812.1580	$812.16	$812.15	$812.10