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	$77.78	7.228%	$83.4019	$83.40	$83.40	$83.40
Purchase #2	$131.47	7.281%	$141.0423	$141.04	$141.05	$141.00
Purchase #3	$184.41	3.874%	$191.554	$191.55	$191.55	$191.60
Purchase #4	$43.32	11.799%	$48.4313	$48.43	$48.45	$48.40
Purchase #5	$130.26	12.207%	$146.1608	$146.16	$146.15	$146.20
Purchase #6	$117.50	5.113%	$123.5078	$123.51	$123.50	$123.50
Purchase #7	$88.36	10.724%	$97.8357	$97.84	$97.85	$97.80
7 purchase totals =	$773.10		$831.9338	$831.93	$831.95	$831.90