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	$72.46	11.528%	$80.8132	$80.81	$80.80	$80.80
Purchase #2	$79.61	8.223%	$86.1563	$86.16	$86.15	$86.20
Purchase #3	$139.46	9.147%	$152.2164	$152.22	$152.20	$152.20
Purchase #4	$45.82	4.596%	$47.9259	$47.93	$47.95	$47.90
Purchase #5	$147.45	10.461%	$162.8747	$162.87	$162.85	$162.90
Purchase #6	$114.46	7.622%	$123.1841	$123.18	$123.20	$123.20
Purchase #7	$40.99	4.615%	$42.8817	$42.88	$42.90	$42.90
7 purchase totals =	$640.25		$696.0523	$696.05	$696.05	$696.10