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	$86.44	13.797%	$98.3661	$98.37	$98.35	$98.40
Purchase #2	$89.90	3.782%	$93.3	$93.30	$93.30	$93.30
Purchase #3	$39.89	10.505%	$44.0804	$44.08	$44.10	$44.10
Purchase #4	$56.74	5.508%	$59.8652	$59.87	$59.85	$59.90
Purchase #5	$247.78	4.191%	$258.1645	$258.16	$258.15	$258.20
Purchase #6	$71.95	8.854%	$78.3205	$78.32	$78.30	$78.30
Purchase #7	$209.31	7.509%	$225.0271	$225.03	$225.05	$225.00
7 purchase totals =	$802.01		$857.1238	$857.13	$857.10	$857.20