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	$8.79	11.740%	$9.8219	$9.82	$9.80	$9.80
Purchase #2	$77.32	8.571%	$83.9471	$83.95	$83.95	$83.90
Purchase #3	$144.72	11.729%	$161.6942	$161.69	$161.70	$161.70
Purchase #4	$95.82	7.614%	$103.1157	$103.12	$103.10	$103.10
Purchase #5	$80.34	12.794%	$90.6187	$90.62	$90.60	$90.60
Purchase #6	$99.37	5.235%	$104.572	$104.57	$104.55	$104.60
Purchase #7	$35.53	4.202%	$37.023	$37.02	$37.00	$37.00
7 purchase totals =	$541.89		$590.7926	$590.79	$590.70	$590.70