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	$66.38	8.703%	$72.1571	$72.16	$72.15	$72.20
Purchase #2	$79.80	4.709%	$83.5578	$83.56	$83.55	$83.60
Purchase #3	$115.87	13.782%	$131.8392	$131.84	$131.85	$131.80
Purchase #4	$246.57	11.528%	$274.9946	$274.99	$275.00	$275.00
Purchase #5	$115.74	7.700%	$124.652	$124.65	$124.65	$124.70
Purchase #6	$19.62	4.642%	$20.5308	$20.53	$20.55	$20.50
Purchase #7	$40.62	11.860%	$45.4375	$45.44	$45.45	$45.40
7 purchase totals =	$684.60		$753.1690	$753.17	$753.20	$753.20