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	$35.78	6.145%	$37.9787	$37.98	$38.00	$38.00
Purchase #2	$165.65	3.425%	$171.3235	$171.32	$171.30	$171.30
Purchase #3	$116.92	9.426%	$127.9409	$127.94	$127.95	$127.90
Purchase #4	$115.87	10.780%	$128.3608	$128.36	$128.35	$128.40
Purchase #5	$162.37	3.697%	$168.3728	$168.37	$168.35	$168.40
Purchase #6	$37.25	3.367%	$38.5042	$38.50	$38.50	$38.50
Purchase #7	$238.49	9.700%	$261.6235	$261.62	$261.60	$261.60
7 purchase totals =	$872.33		$934.1044	$934.09	$934.05	$934.10