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	$99.98	5.582%	$105.5609	$105.56	$105.55	$105.60
Purchase #2	$7.78	9.448%	$8.5151	$8.52	$8.50	$8.50
Purchase #3	$242.72	12.392%	$272.7979	$272.80	$272.80	$272.80
Purchase #4	$215.41	8.133%	$232.9293	$232.93	$232.95	$232.90
Purchase #5	$197.54	5.747%	$208.8926	$208.89	$208.90	$208.90
Purchase #6	$49.56	5.150%	$52.1123	$52.11	$52.10	$52.10
Purchase #7	$218.51	5.740%	$231.0525	$231.05	$231.05	$231.10
7 purchase totals =	$1,031.50		$1,111.8606	$1,111.86	$1,111.85	$1,111.90