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	$39.80	6.288%	$42.3026	$42.30	$42.30	$42.30
Purchase #2	$128.89	13.454%	$146.2309	$146.23	$146.25	$146.20
Purchase #3	$12.38	8.134%	$13.387	$13.39	$13.40	$13.40
Purchase #4	$36.94	6.174%	$39.2207	$39.22	$39.20	$39.20
Purchase #5	$174.99	4.192%	$182.3256	$182.33	$182.35	$182.30
Purchase #6	$173.61	7.217%	$186.1394	$186.14	$186.15	$186.10
Purchase #7	$155.88	11.627%	$174.0042	$174.00	$174.00	$174.00
7 purchase totals =	$722.49		$783.6104	$783.61	$783.65	$783.50