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	$200.75	10.750%	$222.3306	$222.33	$222.35	$222.30
Purchase #2	$104.93	12.579%	$118.1291	$118.13	$118.15	$118.10
Purchase #3	$17.86	13.760%	$20.3175	$20.32	$20.30	$20.30
Purchase #4	$200.35	13.450%	$227.2971	$227.30	$227.30	$227.30
Purchase #5	$134.27	4.609%	$140.4585	$140.46	$140.45	$140.50
Purchase #6	$11.34	6.859%	$12.1178	$12.12	$12.10	$12.10
Purchase #7	$240.29	7.146%	$257.4611	$257.46	$257.45	$257.50
7 purchase totals =	$909.79		$998.1117	$998.12	$998.10	$998.10