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	$249.35	10.696%	$276.0205	$276.02	$276.00	$276.00
Purchase #2	$248.95	6.764%	$265.789	$265.79	$265.80	$265.80
Purchase #3	$200.56	3.715%	$208.0108	$208.01	$208.00	$208.00
Purchase #4	$27.38	5.577%	$28.907	$28.91	$28.90	$28.90
Purchase #5	$24.30	13.435%	$27.5647	$27.56	$27.55	$27.60
Purchase #6	$197.59	10.187%	$217.7185	$217.72	$217.70	$217.70
Purchase #7	$133.46	6.685%	$142.3818	$142.38	$142.40	$142.40
7 purchase totals =	$1,081.59		$1,166.3923	$1,166.39	$1,166.35	$1,166.40