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	$25.53	12.854%	$28.8116	$28.81	$28.80	$28.80
Purchase #2	$34.96	9.143%	$38.1564	$38.16	$38.15	$38.20
Purchase #3	$162.93	11.824%	$182.1948	$182.19	$182.20	$182.20
Purchase #4	$80.60	7.365%	$86.5362	$86.54	$86.55	$86.50
Purchase #5	$131.80	8.294%	$142.7315	$142.73	$142.75	$142.70
Purchase #6	$81.77	4.567%	$85.5044	$85.50	$85.50	$85.50
Purchase #7	$250.77	5.112%	$263.5894	$263.59	$263.60	$263.60
7 purchase totals =	$768.36		$827.5243	$827.52	$827.55	$827.50