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	$35.27	10.630%	$39.0192	$39.02	$39.00	$39.00
Purchase #2	$218.29	4.260%	$227.5892	$227.59	$227.60	$227.60
Purchase #3	$189.58	5.755%	$200.4903	$200.49	$200.50	$200.50
Purchase #4	$153.43	3.786%	$159.2389	$159.24	$159.25	$159.20
Purchase #5	$167.37	3.129%	$172.607	$172.61	$172.60	$172.60
Purchase #6	$53.49	7.677%	$57.5964	$57.60	$57.60	$57.60
Purchase #7	$26.96	6.199%	$28.6313	$28.63	$28.65	$28.60
7 purchase totals =	$844.39		$885.1723	$885.18	$885.20	$885.10