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	$236.91	7.777%	$255.3345	$255.33	$255.35	$255.30
Purchase #2	$167.99	11.817%	$187.8414	$187.84	$187.85	$187.80
Purchase #3	$32.25	12.624%	$36.3212	$36.32	$36.30	$36.30
Purchase #4	$152.48	9.513%	$166.9854	$166.99	$167.00	$167.00
Purchase #5	$100.45	12.354%	$112.8596	$112.86	$112.85	$112.90
Purchase #6	$200.38	9.449%	$219.3139	$219.31	$219.30	$219.30
Purchase #7	$193.92	12.521%	$218.2007	$218.20	$218.20	$218.20
7 purchase totals =	$1,084.38		$1,196.8567	$1,196.85	$1,196.85	$1,196.80