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	$23.82	12.132%	$26.7098	$26.71	$26.70	$26.70
Purchase #2	$11.49	7.731%	$12.3783	$12.38	$12.40	$12.40
Purchase #3	$148.50	12.179%	$166.5858	$166.59	$166.60	$166.60
Purchase #4	$136.39	3.851%	$141.6424	$141.64	$141.65	$141.60
Purchase #5	$123.67	5.676%	$130.6895	$130.69	$130.70	$130.70
Purchase #6	$87.85	3.152%	$90.619	$90.62	$90.60	$90.60
Purchase #7	$236.88	12.234%	$265.8599	$265.86	$265.85	$265.90
7 purchase totals =	$768.60		$834.4847	$834.49	$834.50	$834.50