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	$16.80	10.529%	$18.5689	$18.57	$18.55	$18.60
Purchase #2	$19.86	12.133%	$22.2696	$22.27	$22.25	$22.30
Purchase #3	$143.73	7.872%	$155.0444	$155.04	$155.05	$155.00
Purchase #4	$55.37	7.279%	$59.4004	$59.40	$59.40	$59.40
Purchase #5	$209.63	8.290%	$227.0083	$227.01	$227.00	$227.00
Purchase #6	$47.65	7.761%	$51.3481	$51.35	$51.35	$51.30
Purchase #7	$90.77	11.837%	$101.5144	$101.51	$101.50	$101.50
7 purchase totals =	$583.81		$635.1541	$635.15	$635.10	$635.10