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	$117.72	8.302%	$127.4931	$127.49	$127.50	$127.50
Purchase #2	$100.72	8.156%	$108.9347	$108.93	$108.95	$108.90
Purchase #3	$143.96	9.765%	$158.0177	$158.02	$158.00	$158.00
Purchase #4	$173.29	4.624%	$181.3029	$181.30	$181.30	$181.30
Purchase #5	$44.29	7.319%	$47.5316	$47.53	$47.55	$47.50
Purchase #6	$82.99	3.535%	$85.9237	$85.92	$85.90	$85.90
Purchase #7	$211.35	6.625%	$225.3519	$225.35	$225.35	$225.40
7 purchase totals =	$874.32		$934.5556	$934.54	$934.55	$934.50