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	$232.76	11.225%	$258.8873	$258.89	$258.90	$258.90
Purchase #2	$93.36	7.829%	$100.6692	$100.67	$100.65	$100.70
Purchase #3	$234.31	4.315%	$244.4205	$244.42	$244.40	$244.40
Purchase #4	$29.60	12.619%	$33.3352	$33.34	$33.35	$33.30
Purchase #5	$41.37	10.200%	$45.5897	$45.59	$45.60	$45.60
Purchase #6	$79.41	13.348%	$90.0096	$90.01	$90.00	$90.00
Purchase #7	$185.55	7.645%	$199.7353	$199.74	$199.75	$199.70
7 purchase totals =	$896.36		$972.6468	$972.66	$972.65	$972.60