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	$41.95	9.154%	$45.7901	$45.79	$45.80	$45.80
Purchase #2	$72.50	5.208%	$76.2758	$76.28	$76.30	$76.30
Purchase #3	$242.54	6.645%	$258.6568	$258.66	$258.65	$258.70
Purchase #4	$130.98	4.737%	$137.1845	$137.18	$137.20	$137.20
Purchase #5	$180.36	5.286%	$189.8938	$189.89	$189.90	$189.90
Purchase #6	$37.92	7.746%	$40.8573	$40.86	$40.85	$40.90
Purchase #7	$44.58	12.874%	$50.3192	$50.32	$50.30	$50.30
7 purchase totals =	$750.83		$798.9775	$798.98	$799.00	$799.10