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	$243.52	6.419%	$259.1515	$259.15	$259.15	$259.20
Purchase #2	$167.77	11.602%	$187.2347	$187.23	$187.25	$187.20
Purchase #3	$150.25	12.872%	$169.5902	$169.59	$169.60	$169.60
Purchase #4	$136.44	6.480%	$145.2813	$145.28	$145.30	$145.30
Purchase #5	$109.87	10.389%	$121.2844	$121.28	$121.30	$121.30
Purchase #6	$39.43	8.597%	$42.8198	$42.82	$42.80	$42.80
Purchase #7	$170.86	8.848%	$185.9777	$185.98	$186.00	$186.00
7 purchase totals =	$1,018.14		$1,111.3396	$1,111.33	$1,111.40	$1,111.40