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	$19.57	5.518%	$20.6499	$20.65	$20.65	$20.60
Purchase #2	$184.25	3.578%	$190.8425	$190.84	$190.85	$190.80
Purchase #3	$124.91	9.597%	$136.8976	$136.90	$136.90	$136.90
Purchase #4	$145.52	11.676%	$162.5109	$162.51	$162.50	$162.50
Purchase #5	$104.81	10.157%	$115.4556	$115.46	$115.45	$115.50
Purchase #6	$37.45	6.821%	$40.0045	$40.00	$40.00	$40.00
Purchase #7	$203.98	10.706%	$225.8181	$225.82	$225.80	$225.80
7 purchase totals =	$820.49		$892.1791	$892.18	$892.15	$892.10