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	$136.31	8.689%	$148.154	$148.15	$148.15	$148.20
Purchase #2	$210.51	5.654%	$222.4122	$222.41	$222.40	$222.40
Purchase #3	$133.61	6.210%	$141.9072	$141.91	$141.90	$141.90
Purchase #4	$46.49	11.785%	$51.9688	$51.97	$51.95	$52.00
Purchase #5	$130.46	8.792%	$141.93	$141.93	$141.95	$141.90
Purchase #6	$34.25	7.710%	$36.8907	$36.89	$36.90	$36.90
Purchase #7	$174.59	10.721%	$193.3078	$193.31	$193.30	$193.30
7 purchase totals =	$866.22		$936.5707	$936.57	$936.55	$936.60