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	$170.87	9.660%	$187.376	$187.38	$187.40	$187.40
Purchase #2	$161.89	6.131%	$171.8155	$171.82	$171.80	$171.80
Purchase #3	$166.67	3.458%	$172.4334	$172.43	$172.45	$172.40
Purchase #4	$133.48	12.311%	$149.9127	$149.91	$149.90	$149.90
Purchase #5	$30.87	11.700%	$34.4818	$34.48	$34.50	$34.50
Purchase #6	$116.58	6.116%	$123.71	$123.71	$123.70	$123.70
Purchase #7	$154.76	9.473%	$169.4204	$169.42	$169.40	$169.40
7 purchase totals =	$935.12		$1,009.1498	$1,009.15	$1,009.15	$1,009.10