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	$139.26	12.553%	$156.7413	$156.74	$156.75	$156.70
Purchase #2	$99.35	10.617%	$109.898	$109.90	$109.90	$109.90
Purchase #3	$98.90	10.828%	$109.6089	$109.61	$109.60	$109.60
Purchase #4	$42.98	5.550%	$45.3654	$45.37	$45.35	$45.40
Purchase #5	$20.81	4.324%	$21.7098	$21.71	$21.70	$21.70
Purchase #6	$134.51	11.738%	$150.2988	$150.30	$150.30	$150.30
Purchase #7	$83.54	9.288%	$91.2992	$91.30	$91.30	$91.30
7 purchase totals =	$619.35		$684.9214	$684.93	$684.90	$684.90