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	$137.40	9.816%	$150.8872	$150.89	$150.90	$150.90
Purchase #2	$103.96	3.206%	$107.293	$107.29	$107.30	$107.30
Purchase #3	$243.61	13.507%	$276.5144	$276.51	$276.50	$276.50
Purchase #4	$44.82	13.311%	$50.786	$50.79	$50.80	$50.80
Purchase #5	$72.71	8.731%	$79.0583	$79.06	$79.05	$79.10
Purchase #6	$80.71	6.465%	$85.9279	$85.93	$85.95	$85.90
Purchase #7	$79.45	13.725%	$90.3545	$90.35	$90.35	$90.40
7 purchase totals =	$762.66		$840.8213	$840.82	$840.85	$840.90