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	$36.94	10.614%	$40.8608	$40.86	$40.85	$40.90
Purchase #2	$220.27	4.344%	$229.8385	$229.84	$229.85	$229.80
Purchase #3	$48.54	12.801%	$54.7536	$54.75	$54.75	$54.80
Purchase #4	$186.59	5.396%	$196.6584	$196.66	$196.65	$196.70
Purchase #5	$157.44	11.484%	$175.5204	$175.52	$175.50	$175.50
Purchase #6	$104.78	12.545%	$117.9247	$117.92	$117.90	$117.90
Purchase #7	$19.26	11.107%	$21.3992	$21.40	$21.40	$21.40
7 purchase totals =	$773.82		$836.9556	$836.95	$836.90	$837.00