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	$222.70	12.687%	$250.9539	$250.95	$250.95	$251.00
Purchase #2	$135.56	10.827%	$150.2371	$150.24	$150.25	$150.20
Purchase #3	$206.64	5.259%	$217.5072	$217.51	$217.50	$217.50
Purchase #4	$83.28	3.834%	$86.473	$86.47	$86.45	$86.50
Purchase #5	$38.65	7.706%	$41.6284	$41.63	$41.65	$41.60
Purchase #6	$38.92	13.598%	$44.2123	$44.21	$44.20	$44.20
Purchase #7	$189.97	3.412%	$196.4518	$196.45	$196.45	$196.50
7 purchase totals =	$915.72		$987.4637	$987.46	$987.45	$987.50