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	$132.64	10.630%	$146.7396	$146.74	$146.75	$146.70
Purchase #2	$42.61	5.211%	$44.8304	$44.83	$44.85	$44.80
Purchase #3	$94.69	9.286%	$103.4829	$103.48	$103.50	$103.50
Purchase #4	$216.79	12.815%	$244.5716	$244.57	$244.55	$244.60
Purchase #5	$71.95	12.863%	$81.2049	$81.20	$81.20	$81.20
Purchase #6	$73.57	7.298%	$78.9391	$78.94	$78.95	$78.90
Purchase #7	$167.89	4.751%	$175.8665	$175.87	$175.85	$175.90
7 purchase totals =	$800.14		$875.6350	$875.63	$875.65	$875.60