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	$29.79	11.523%	$33.2227	$33.22	$33.20	$33.20
Purchase #2	$50.41	13.646%	$57.2889	$57.29	$57.30	$57.30
Purchase #3	$81.33	10.160%	$89.5931	$89.59	$89.60	$89.60
Purchase #4	$99.46	6.134%	$105.5609	$105.56	$105.55	$105.60
Purchase #5	$156.98	9.184%	$171.397	$171.40	$171.40	$171.40
Purchase #6	$94.49	5.810%	$99.9799	$99.98	$100.00	$100.00
Purchase #7	$202.74	9.181%	$221.3536	$221.35	$221.35	$221.40
7 purchase totals =	$715.20		$778.3961	$778.39	$778.40	$778.50