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	$107.46	5.571%	$113.4466	$113.45	$113.45	$113.40
Purchase #2	$100.38	4.442%	$104.8389	$104.84	$104.85	$104.80
Purchase #3	$73.82	12.123%	$82.7692	$82.77	$82.75	$82.80
Purchase #4	$111.33	9.518%	$121.9264	$121.93	$121.95	$121.90
Purchase #5	$34.89	12.368%	$39.2052	$39.21	$39.20	$39.20
Purchase #6	$175.90	11.650%	$196.3924	$196.39	$196.40	$196.40
Purchase #7	$144.37	11.337%	$160.7372	$160.74	$160.75	$160.70
7 purchase totals =	$748.15		$819.3159	$819.33	$819.35	$819.20