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	$42.95	6.741%	$45.8453	$45.85	$45.85	$45.80
Purchase #2	$95.81	13.819%	$109.05	$109.05	$109.05	$109.10
Purchase #3	$23.35	5.231%	$24.5714	$24.57	$24.55	$24.60
Purchase #4	$139.43	3.690%	$144.575	$144.58	$144.60	$144.60
Purchase #5	$222.69	9.199%	$243.1753	$243.18	$243.20	$243.20
Purchase #6	$16.69	10.358%	$18.4188	$18.42	$18.40	$18.40
Purchase #7	$80.81	13.230%	$91.5012	$91.50	$91.50	$91.50
7 purchase totals =	$621.73		$677.1370	$677.15	$677.15	$677.20