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	$123.43	11.717%	$137.8923	$137.89	$137.90	$137.90
Purchase #2	$33.56	12.719%	$37.8285	$37.83	$37.85	$37.80
Purchase #3	$182.25	9.355%	$199.2995	$199.30	$199.30	$199.30
Purchase #4	$187.76	5.740%	$198.5374	$198.54	$198.55	$198.50
Purchase #5	$106.70	10.328%	$117.72	$117.72	$117.70	$117.70
Purchase #6	$99.88	5.139%	$105.0128	$105.01	$105.00	$105.00
Purchase #7	$237.92	10.198%	$262.1831	$262.18	$262.20	$262.20
7 purchase totals =	$971.50		$1,058.4736	$1,058.47	$1,058.50	$1,058.40