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	$91.25	12.448%	$102.6088	$102.61	$102.60	$102.60
Purchase #2	$160.48	4.820%	$168.2151	$168.22	$168.20	$168.20
Purchase #3	$141.64	3.458%	$146.5379	$146.54	$146.55	$146.50
Purchase #4	$203.82	5.503%	$215.0362	$215.04	$215.05	$215.00
Purchase #5	$83.59	11.308%	$93.0424	$93.04	$93.05	$93.00
Purchase #6	$74.81	9.137%	$81.6454	$81.65	$81.65	$81.60
Purchase #7	$86.45	4.641%	$90.4621	$90.46	$90.45	$90.50
7 purchase totals =	$842.04		$897.5479	$897.56	$897.55	$897.40