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	$52.25	10.636%	$57.8073	$57.81	$57.80	$57.80
Purchase #2	$150.54	13.263%	$170.5061	$170.51	$170.50	$170.50
Purchase #3	$199.37	8.790%	$216.8946	$216.89	$216.90	$216.90
Purchase #4	$195.53	13.782%	$222.4779	$222.48	$222.50	$222.50
Purchase #5	$99.30	3.444%	$102.7199	$102.72	$102.70	$102.70
Purchase #6	$82.91	7.534%	$89.1564	$89.16	$89.15	$89.20
Purchase #7	$95.32	13.280%	$107.9785	$107.98	$108.00	$108.00
7 purchase totals =	$875.22		$967.5407	$967.55	$967.55	$967.60