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	$85.96	13.416%	$97.4924	$97.49	$97.50	$97.50
Purchase #2	$36.34	6.809%	$38.8144	$38.81	$38.80	$38.80
Purchase #3	$99.26	4.676%	$103.9014	$103.90	$103.90	$103.90
Purchase #4	$189.47	13.865%	$215.74	$215.74	$215.75	$215.70
Purchase #5	$101.40	4.438%	$105.9001	$105.90	$105.90	$105.90
Purchase #6	$78.73	5.710%	$83.2255	$83.23	$83.25	$83.20
Purchase #7	$119.45	9.594%	$130.91	$130.91	$130.90	$130.90
7 purchase totals =	$710.61		$775.9838	$775.98	$776.00	$775.90