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	$232.86	6.175%	$247.2391	$247.24	$247.25	$247.20
Purchase #2	$41.31	5.222%	$43.4672	$43.47	$43.45	$43.50
Purchase #3	$201.77	10.435%	$222.8247	$222.82	$222.80	$222.80
Purchase #4	$7.39	12.832%	$8.3383	$8.34	$8.35	$8.30
Purchase #5	$129.59	13.443%	$147.0108	$147.01	$147.00	$147.00
Purchase #6	$235.64	13.380%	$267.1686	$267.17	$267.15	$267.20
Purchase #7	$89.78	12.410%	$100.9217	$100.92	$100.90	$100.90
7 purchase totals =	$938.34		$1,036.9704	$1,036.97	$1,036.90	$1,036.90