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	$237.50	10.511%	$262.4636	$262.46	$262.45	$262.50
Purchase #2	$121.89	5.576%	$128.6866	$128.69	$128.70	$128.70
Purchase #3	$204.59	10.227%	$225.5134	$225.51	$225.50	$225.50
Purchase #4	$177.39	8.457%	$192.3919	$192.39	$192.40	$192.40
Purchase #5	$155.50	12.617%	$175.1194	$175.12	$175.10	$175.10
Purchase #6	$35.40	6.804%	$37.8086	$37.81	$37.80	$37.80
Purchase #7	$125.90	9.236%	$137.5281	$137.53	$137.55	$137.50
7 purchase totals =	$1,058.17		$1,159.5116	$1,159.51	$1,159.50	$1,159.50