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	$239.48	8.343%	$259.4598	$259.46	$259.45	$259.50
Purchase #2	$18.71	6.770%	$19.9767	$19.98	$20.00	$20.00
Purchase #3	$152.91	12.390%	$171.8555	$171.86	$171.85	$171.90
Purchase #4	$58.99	8.520%	$64.0159	$64.02	$64.00	$64.00
Purchase #5	$124.59	13.813%	$141.7996	$141.80	$141.80	$141.80
Purchase #6	$80.95	10.647%	$89.5687	$89.57	$89.55	$89.60
Purchase #7	$158.87	11.300%	$176.8223	$176.82	$176.80	$176.80
7 purchase totals =	$834.50		$923.4985	$923.51	$923.45	$923.60