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	$83.88	7.417%	$90.1014	$90.10	$90.10	$90.10
Purchase #2	$250.54	13.739%	$284.9617	$284.96	$284.95	$285.00
Purchase #3	$148.37	12.562%	$167.0082	$167.01	$167.00	$167.00
Purchase #4	$42.76	10.705%	$47.3375	$47.34	$47.35	$47.30
Purchase #5	$109.58	12.462%	$123.2359	$123.24	$123.25	$123.20
Purchase #6	$192.65	3.264%	$198.9381	$198.94	$198.95	$198.90
Purchase #7	$136.81	10.722%	$151.4788	$151.48	$151.50	$151.50
7 purchase totals =	$964.59		$1,063.0616	$1,063.07	$1,063.10	$1,063.00