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	$38.44	4.584%	$40.2021	$40.20	$40.20	$40.20
Purchase #2	$183.77	11.507%	$204.9164	$204.92	$204.90	$204.90
Purchase #3	$206.54	6.577%	$220.1241	$220.12	$220.10	$220.10
Purchase #4	$146.91	11.729%	$164.1411	$164.14	$164.15	$164.10
Purchase #5	$123.49	10.570%	$136.5429	$136.54	$136.55	$136.50
Purchase #6	$100.87	4.160%	$105.0662	$105.07	$105.05	$105.10
Purchase #7	$214.77	3.383%	$222.0357	$222.04	$222.05	$222.00
7 purchase totals =	$1,014.79		$1,093.0285	$1,093.03	$1,093.00	$1,092.90