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	$8.59	3.800%	$8.9164	$8.92	$8.90	$8.90
Purchase #2	$57.27	4.387%	$59.7824	$59.78	$59.80	$59.80
Purchase #3	$166.27	7.626%	$178.9498	$178.95	$178.95	$178.90
Purchase #4	$150.60	3.710%	$156.1873	$156.19	$156.20	$156.20
Purchase #5	$150.34	12.837%	$169.6391	$169.64	$169.65	$169.60
Purchase #6	$169.73	9.280%	$185.4809	$185.48	$185.50	$185.50
Purchase #7	$85.98	8.212%	$93.0407	$93.04	$93.05	$93.00
7 purchase totals =	$788.78		$851.9966	$852.00	$852.05	$851.90