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	$6.70	13.118%	$7.5789	$7.58	$7.60	$7.60
Purchase #2	$130.88	11.744%	$146.2505	$146.25	$146.25	$146.30
Purchase #3	$11.63	5.287%	$12.2449	$12.24	$12.25	$12.20
Purchase #4	$198.59	5.361%	$209.2364	$209.24	$209.25	$209.20
Purchase #5	$199.91	5.537%	$210.979	$210.98	$211.00	$211.00
Purchase #6	$81.32	11.799%	$90.9149	$90.91	$90.90	$90.90
Purchase #7	$64.94	10.687%	$71.8801	$71.88	$71.90	$71.90
7 purchase totals =	$693.97		$749.0847	$749.08	$749.15	$749.10