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	$99.56	10.254%	$109.7689	$109.77	$109.75	$109.80
Purchase #2	$201.89	10.473%	$223.0339	$223.03	$223.05	$223.00
Purchase #3	$123.65	13.759%	$140.663	$140.66	$140.65	$140.70
Purchase #4	$76.41	9.457%	$83.6361	$83.64	$83.65	$83.60
Purchase #5	$146.42	4.463%	$152.9547	$152.95	$152.95	$153.00
Purchase #6	$54.88	4.176%	$57.1718	$57.17	$57.15	$57.20
Purchase #7	$19.94	8.768%	$21.6883	$21.69	$21.70	$21.70
7 purchase totals =	$722.75		$788.9167	$788.91	$788.90	$789.00