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	$117.34	5.522%	$123.8195	$123.82	$123.80	$123.80
Purchase #2	$37.73	9.273%	$41.2287	$41.23	$41.25	$41.20
Purchase #3	$18.29	12.677%	$20.6086	$20.61	$20.60	$20.60
Purchase #4	$147.47	5.429%	$155.4761	$155.48	$155.50	$155.50
Purchase #5	$31.85	6.227%	$33.8333	$33.83	$33.85	$33.80
Purchase #6	$222.34	9.575%	$243.6291	$243.63	$243.65	$243.60
Purchase #7	$152.34	12.416%	$171.2545	$171.25	$171.25	$171.30
7 purchase totals =	$727.36		$789.8498	$789.85	$789.90	$789.80