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	$226.59	13.347%	$256.833	$256.83	$256.85	$256.80
Purchase #2	$41.33	4.475%	$43.1795	$43.18	$43.20	$43.20
Purchase #3	$222.40	11.611%	$248.2229	$248.22	$248.20	$248.20
Purchase #4	$25.92	11.397%	$28.8741	$28.87	$28.85	$28.90
Purchase #5	$151.43	8.769%	$164.7089	$164.71	$164.70	$164.70
Purchase #6	$94.73	8.496%	$102.7783	$102.78	$102.80	$102.80
Purchase #7	$67.56	4.481%	$70.5874	$70.59	$70.60	$70.60
7 purchase totals =	$829.96		$915.1841	$915.18	$915.20	$915.20