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	$26.61	5.645%	$28.1121	$28.11	$28.10	$28.10
Purchase #2	$112.27	10.262%	$123.7911	$123.79	$123.80	$123.80
Purchase #3	$112.90	3.270%	$116.5918	$116.59	$116.60	$116.60
Purchase #4	$152.34	5.212%	$160.28	$160.28	$160.30	$160.30
Purchase #5	$75.35	4.449%	$78.7023	$78.70	$78.70	$78.70
Purchase #6	$127.50	11.523%	$142.1918	$142.19	$142.20	$142.20
Purchase #7	$110.58	4.155%	$115.1746	$115.17	$115.15	$115.20
7 purchase totals =	$717.55		$764.8437	$764.83	$764.85	$764.90