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	$167.65	11.673%	$187.2198	$187.22	$187.20	$187.20
Purchase #2	$119.71	9.301%	$130.8442	$130.84	$130.85	$130.80
Purchase #3	$111.83	10.731%	$123.8305	$123.83	$123.85	$123.80
Purchase #4	$92.49	6.241%	$98.2623	$98.26	$98.25	$98.30
Purchase #5	$161.38	3.747%	$167.4269	$167.43	$167.45	$167.40
Purchase #6	$158.62	5.628%	$167.5471	$167.55	$167.55	$167.50
Purchase #7	$39.83	5.570%	$42.0485	$42.05	$42.05	$42.00
7 purchase totals =	$851.51		$917.1793	$917.18	$917.20	$917.00