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	$25.68	11.126%	$28.5372	$28.54	$28.55	$28.50
Purchase #2	$31.29	13.632%	$35.5555	$35.56	$35.55	$35.60
Purchase #3	$163.96	4.506%	$171.348	$171.35	$171.35	$171.30
Purchase #4	$138.66	9.680%	$152.0823	$152.08	$152.10	$152.10
Purchase #5	$93.66	7.506%	$100.6901	$100.69	$100.70	$100.70
Purchase #6	$58.37	9.811%	$64.0967	$64.10	$64.10	$64.10
Purchase #7	$196.92	10.825%	$218.2366	$218.24	$218.25	$218.20
7 purchase totals =	$708.54		$770.5464	$770.56	$770.60	$770.50