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	$6.63	8.348%	$7.1835	$7.18	$7.20	$7.20
Purchase #2	$179.75	9.354%	$196.5638	$196.56	$196.55	$196.60
Purchase #3	$101.82	11.429%	$113.457	$113.46	$113.45	$113.50
Purchase #4	$48.90	13.504%	$55.5035	$55.50	$55.50	$55.50
Purchase #5	$138.76	5.380%	$146.2253	$146.23	$146.25	$146.20
Purchase #6	$190.76	10.151%	$210.124	$210.12	$210.10	$210.10
Purchase #7	$186.96	5.200%	$196.6819	$196.68	$196.70	$196.70
7 purchase totals =	$853.58		$925.7390	$925.73	$925.75	$925.80