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	$86.32	3.592%	$89.4206	$89.42	$89.40	$89.40
Purchase #2	$39.55	10.739%	$43.7973	$43.80	$43.80	$43.80
Purchase #3	$144.61	12.235%	$162.303	$162.30	$162.30	$162.30
Purchase #4	$54.31	7.442%	$58.3518	$58.35	$58.35	$58.40
Purchase #5	$193.97	5.805%	$205.23	$205.23	$205.25	$205.20
Purchase #6	$244.86	6.748%	$261.3832	$261.38	$261.40	$261.40
Purchase #7	$63.59	13.304%	$72.05	$72.05	$72.05	$72.10
7 purchase totals =	$827.21		$892.5359	$892.53	$892.55	$892.60