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	$37.43	3.656%	$38.7984	$38.80	$38.80	$38.80
Purchase #2	$82.36	5.549%	$86.9302	$86.93	$86.95	$86.90
Purchase #3	$27.94	13.756%	$31.7834	$31.78	$31.80	$31.80
Purchase #4	$139.59	12.232%	$156.6646	$156.66	$156.65	$156.70
Purchase #5	$103.71	4.117%	$107.9797	$107.98	$108.00	$108.00
Purchase #6	$14.64	3.482%	$15.1498	$15.15	$15.15	$15.10
Purchase #7	$104.89	13.370%	$118.9138	$118.91	$118.90	$118.90
7 purchase totals =	$510.56		$556.2199	$556.21	$556.25	$556.20