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	$154.63	7.859%	$166.7824	$166.78	$166.80	$166.80
Purchase #2	$36.81	12.482%	$41.4046	$41.40	$41.40	$41.40
Purchase #3	$244.48	8.228%	$264.5958	$264.60	$264.60	$264.60
Purchase #4	$45.63	13.558%	$51.8165	$51.82	$51.80	$51.80
Purchase #5	$246.90	11.278%	$274.7454	$274.75	$274.75	$274.70
Purchase #6	$216.72	10.244%	$238.9208	$238.92	$238.90	$238.90
Purchase #7	$90.33	11.582%	$100.792	$100.79	$100.80	$100.80
7 purchase totals =	$1,035.50		$1,139.0575	$1,139.06	$1,139.05	$1,139.00