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	$20.57	3.573%	$21.305	$21.31	$21.30	$21.30
Purchase #2	$131.36	4.595%	$137.396	$137.40	$137.40	$137.40
Purchase #3	$53.34	11.213%	$59.321	$59.32	$59.30	$59.30
Purchase #4	$204.82	9.255%	$223.7761	$223.78	$223.80	$223.80
Purchase #5	$65.37	6.171%	$69.404	$69.40	$69.40	$69.40
Purchase #6	$210.92	8.699%	$229.2679	$229.27	$229.25	$229.30
Purchase #7	$189.48	12.622%	$213.3962	$213.40	$213.40	$213.40
7 purchase totals =	$875.86		$953.8662	$953.88	$953.85	$953.90