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	$25.79	6.367%	$27.432	$27.43	$27.45	$27.40
Purchase #2	$108.29	13.603%	$123.0207	$123.02	$123.00	$123.00
Purchase #3	$79.97	6.309%	$85.0153	$85.02	$85.00	$85.00
Purchase #4	$240.35	12.321%	$269.9635	$269.96	$269.95	$270.00
Purchase #5	$160.52	6.622%	$171.1496	$171.15	$171.15	$171.10
Purchase #6	$127.79	12.132%	$143.2935	$143.29	$143.30	$143.30
Purchase #7	$117.58	10.809%	$130.2892	$130.29	$130.30	$130.30
7 purchase totals =	$860.29		$950.1638	$950.16	$950.15	$950.10