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	$214.69	5.785%	$227.1098	$227.11	$227.10	$227.10
Purchase #2	$45.59	12.581%	$51.3257	$51.33	$51.35	$51.30
Purchase #3	$64.41	12.626%	$72.5424	$72.54	$72.55	$72.50
Purchase #4	$56.29	11.626%	$62.8343	$62.83	$62.85	$62.80
Purchase #5	$180.45	6.427%	$192.0475	$192.05	$192.05	$192.00
Purchase #6	$157.32	9.401%	$172.1097	$172.11	$172.10	$172.10
Purchase #7	$106.86	5.181%	$112.3964	$112.40	$112.40	$112.40
7 purchase totals =	$825.61		$890.3658	$890.37	$890.40	$890.20