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	$81.42	10.840%	$90.2459	$90.25	$90.25	$90.20
Purchase #2	$217.38	8.473%	$235.7986	$235.80	$235.80	$235.80
Purchase #3	$179.86	5.556%	$189.853	$189.85	$189.85	$189.90
Purchase #4	$51.25	12.618%	$57.7167	$57.72	$57.70	$57.70
Purchase #5	$80.64	13.813%	$91.7788	$91.78	$91.80	$91.80
Purchase #6	$44.32	3.384%	$45.8198	$45.82	$45.80	$45.80
Purchase #7	$135.25	13.668%	$153.736	$153.74	$153.75	$153.70
7 purchase totals =	$790.12		$864.9488	$864.96	$864.95	$864.90