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	$138.46	10.737%	$153.3265	$153.33	$153.35	$153.30
Purchase #2	$196.54	3.481%	$203.3816	$203.38	$203.40	$203.40
Purchase #3	$37.26	11.618%	$41.5889	$41.59	$41.60	$41.60
Purchase #4	$189.82	10.650%	$210.0358	$210.04	$210.05	$210.00
Purchase #5	$246.87	11.304%	$274.7762	$274.78	$274.80	$274.80
Purchase #6	$41.27	10.572%	$45.6331	$45.63	$45.65	$45.60
Purchase #7	$33.72	10.732%	$37.3388	$37.34	$37.35	$37.30
7 purchase totals =	$883.94		$966.0809	$966.09	$966.20	$966.00