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	$90.72	7.481%	$97.5068	$97.51	$97.50	$97.50
Purchase #2	$119.97	9.227%	$131.0396	$131.04	$131.05	$131.00
Purchase #3	$64.61	13.219%	$73.1508	$73.15	$73.15	$73.20
Purchase #4	$134.50	4.743%	$140.8793	$140.88	$140.90	$140.90
Purchase #5	$43.68	4.398%	$45.601	$45.60	$45.60	$45.60
Purchase #6	$149.57	13.577%	$169.8771	$169.88	$169.90	$169.90
Purchase #7	$144.65	12.321%	$162.4723	$162.47	$162.45	$162.50
7 purchase totals =	$747.70		$820.5269	$820.53	$820.55	$820.60