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	$13.46	3.253%	$13.8979	$13.90	$13.90	$13.90
Purchase #2	$228.62	13.680%	$259.8952	$259.90	$259.90	$259.90
Purchase #3	$6.62	9.145%	$7.2254	$7.23	$7.25	$7.20
Purchase #4	$81.69	5.251%	$85.9795	$85.98	$86.00	$86.00
Purchase #5	$90.49	12.597%	$101.889	$101.89	$101.90	$101.90
Purchase #6	$197.84	9.596%	$216.8247	$216.82	$216.80	$216.80
Purchase #7	$104.60	13.141%	$118.3455	$118.35	$118.35	$118.30
7 purchase totals =	$723.32		$804.0572	$804.07	$804.10	$804.00