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	$21.68	5.415%	$22.854	$22.85	$22.85	$22.90
Purchase #2	$116.60	11.400%	$129.8924	$129.89	$129.90	$129.90
Purchase #3	$45.95	13.240%	$52.0338	$52.03	$52.05	$52.00
Purchase #4	$90.28	9.797%	$99.1247	$99.12	$99.10	$99.10
Purchase #5	$223.93	9.441%	$245.0712	$245.07	$245.05	$245.10
Purchase #6	$81.61	8.847%	$88.83	$88.83	$88.85	$88.80
Purchase #7	$48.29	4.671%	$50.5456	$50.55	$50.55	$50.50
7 purchase totals =	$628.34		$688.3517	$688.34	$688.35	$688.30