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	$87.55	10.681%	$96.9012	$96.90	$96.90	$96.90
Purchase #2	$207.96	7.290%	$223.1203	$223.12	$223.10	$223.10
Purchase #3	$50.29	5.630%	$53.1213	$53.12	$53.10	$53.10
Purchase #4	$214.80	3.359%	$222.0151	$222.02	$222.00	$222.00
Purchase #5	$96.39	4.704%	$100.9242	$100.92	$100.90	$100.90
Purchase #6	$178.41	9.308%	$195.0164	$195.02	$195.00	$195.00
Purchase #7	$92.63	10.370%	$102.2357	$102.24	$102.25	$102.20
7 purchase totals =	$928.03		$993.3342	$993.34	$993.25	$993.20