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	$73.95	7.617%	$79.5828	$79.58	$79.60	$79.60
Purchase #2	$56.27	5.423%	$59.3215	$59.32	$59.30	$59.30
Purchase #3	$221.30	13.228%	$250.5736	$250.57	$250.55	$250.60
Purchase #4	$36.81	4.756%	$38.5607	$38.56	$38.55	$38.60
Purchase #5	$152.70	6.454%	$162.5553	$162.56	$162.55	$162.60
Purchase #6	$44.70	9.524%	$48.9572	$48.96	$48.95	$49.00
Purchase #7	$70.85	9.222%	$77.3838	$77.38	$77.40	$77.40
7 purchase totals =	$656.58		$716.9349	$716.93	$716.90	$717.10