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	$85.80	5.526%	$90.5413	$90.54	$90.55	$90.50
Purchase #2	$65.44	11.187%	$72.7608	$72.76	$72.75	$72.80
Purchase #3	$233.66	6.629%	$249.1493	$249.15	$249.15	$249.10
Purchase #4	$129.38	11.855%	$144.718	$144.72	$144.70	$144.70
Purchase #5	$161.53	11.398%	$179.9412	$179.94	$179.95	$179.90
Purchase #6	$175.90	13.667%	$199.9403	$199.94	$199.95	$199.90
Purchase #7	$152.76	5.197%	$160.6989	$160.70	$160.70	$160.70
7 purchase totals =	$1,004.47		$1,097.7498	$1,097.75	$1,097.75	$1,097.60