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	$156.58	8.209%	$169.4337	$169.43	$169.45	$169.40
Purchase #2	$150.47	12.174%	$168.7882	$168.79	$168.80	$168.80
Purchase #3	$38.54	12.686%	$43.4292	$43.43	$43.45	$43.40
Purchase #4	$119.40	10.118%	$131.4809	$131.48	$131.50	$131.50
Purchase #5	$45.35	7.454%	$48.7304	$48.73	$48.75	$48.70
Purchase #6	$196.57	13.203%	$222.5231	$222.52	$222.50	$222.50
Purchase #7	$203.67	3.348%	$210.4889	$210.49	$210.50	$210.50
7 purchase totals =	$910.58		$994.8744	$994.87	$994.95	$994.80