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	$27.90	3.141%	$28.7763	$28.78	$28.80	$28.80
Purchase #2	$145.76	11.597%	$162.6638	$162.66	$162.65	$162.70
Purchase #3	$59.71	13.739%	$67.9136	$67.91	$67.90	$67.90
Purchase #4	$212.32	13.535%	$241.0575	$241.06	$241.05	$241.10
Purchase #5	$24.88	10.121%	$27.3981	$27.40	$27.40	$27.40
Purchase #6	$78.42	4.302%	$81.7936	$81.79	$81.80	$81.80
Purchase #7	$33.53	7.850%	$36.1621	$36.16	$36.15	$36.20
7 purchase totals =	$582.52		$645.7650	$645.76	$645.75	$645.90