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	$90.92	10.570%	$100.5302	$100.53	$100.55	$100.50
Purchase #2	$184.57	6.234%	$196.0761	$196.08	$196.10	$196.10
Purchase #3	$218.48	6.180%	$231.9821	$231.98	$232.00	$232.00
Purchase #4	$170.42	12.774%	$192.1895	$192.19	$192.20	$192.20
Purchase #5	$199.33	9.355%	$217.9773	$217.98	$218.00	$218.00
Purchase #6	$15.37	12.536%	$17.2968	$17.30	$17.30	$17.30
Purchase #7	$20.45	6.592%	$21.7981	$21.80	$21.80	$21.80
7 purchase totals =	$899.54		$977.8501	$977.86	$977.95	$977.90