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	$139.92	4.851%	$146.7075	$146.71	$146.70	$146.70
Purchase #2	$40.56	12.606%	$45.673	$45.67	$45.65	$45.70
Purchase #3	$55.50	7.779%	$59.8173	$59.82	$59.80	$59.80
Purchase #4	$121.63	8.103%	$131.4857	$131.49	$131.50	$131.50
Purchase #5	$103.79	8.153%	$112.252	$112.25	$112.25	$112.30
Purchase #6	$243.34	8.273%	$263.4715	$263.47	$263.45	$263.50
Purchase #7	$7.36	11.513%	$8.2074	$8.21	$8.20	$8.20
7 purchase totals =	$712.10		$767.6144	$767.62	$767.55	$767.70