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	$157.62	3.112%	$162.5251	$162.53	$162.55	$162.50
Purchase #2	$119.72	7.104%	$128.2249	$128.22	$128.20	$128.20
Purchase #3	$83.77	6.325%	$89.0685	$89.07	$89.05	$89.10
Purchase #4	$172.39	10.591%	$190.6478	$190.65	$190.65	$190.60
Purchase #5	$161.49	6.181%	$171.4717	$171.47	$171.45	$171.50
Purchase #6	$33.91	7.203%	$36.3525	$36.35	$36.35	$36.40
Purchase #7	$38.38	13.120%	$43.4155	$43.42	$43.40	$43.40
7 purchase totals =	$767.28		$821.7060	$821.71	$821.65	$821.70