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	$186.39	13.655%	$211.8416	$211.84	$211.85	$211.80
Purchase #2	$87.83	7.299%	$94.2407	$94.24	$94.25	$94.20
Purchase #3	$151.38	3.565%	$156.7767	$156.78	$156.80	$156.80
Purchase #4	$49.35	9.315%	$53.947	$53.95	$53.95	$53.90
Purchase #5	$90.92	10.796%	$100.7357	$100.74	$100.75	$100.70
Purchase #6	$138.90	12.244%	$155.9069	$155.91	$155.90	$155.90
Purchase #7	$208.48	10.362%	$230.0827	$230.08	$230.10	$230.10
7 purchase totals =	$913.25		$1,003.5313	$1,003.54	$1,003.60	$1,003.40