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	$76.93	4.691%	$80.5388	$80.54	$80.55	$80.50
Purchase #2	$61.92	6.379%	$65.8699	$65.87	$65.85	$65.90
Purchase #3	$51.97	11.624%	$58.011	$58.01	$58.00	$58.00
Purchase #4	$247.51	12.790%	$279.1665	$279.17	$279.15	$279.20
Purchase #5	$147.87	13.254%	$167.4687	$167.47	$167.45	$167.50
Purchase #6	$166.88	11.795%	$186.5635	$186.56	$186.55	$186.60
Purchase #7	$43.79	4.289%	$45.6682	$45.67	$45.65	$45.70
7 purchase totals =	$796.87		$883.2866	$883.29	$883.20	$883.40