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	$59.73	3.645%	$61.9072	$61.91	$61.90	$61.90
Purchase #2	$56.81	11.209%	$63.1778	$63.18	$63.20	$63.20
Purchase #3	$136.59	9.768%	$149.9321	$149.93	$149.95	$149.90
Purchase #4	$83.86	7.386%	$90.0539	$90.05	$90.05	$90.10
Purchase #5	$58.95	12.294%	$66.1973	$66.20	$66.20	$66.20
Purchase #6	$240.89	13.569%	$273.5764	$273.58	$273.60	$273.60
Purchase #7	$211.86	9.238%	$231.4316	$231.43	$231.45	$231.40
7 purchase totals =	$848.69		$936.2763	$936.28	$936.35	$936.30