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	$123.76	3.538%	$128.1386	$128.14	$128.15	$128.10
Purchase #2	$231.25	11.777%	$258.4843	$258.48	$258.50	$258.50
Purchase #3	$164.40	8.400%	$178.2096	$178.21	$178.20	$178.20
Purchase #4	$128.65	12.553%	$144.7994	$144.80	$144.80	$144.80
Purchase #5	$86.44	11.455%	$96.3417	$96.34	$96.35	$96.30
Purchase #6	$31.61	4.512%	$33.0362	$33.04	$33.05	$33.00
Purchase #7	$127.96	8.681%	$139.0682	$139.07	$139.05	$139.10
7 purchase totals =	$894.07		$978.0780	$978.08	$978.10	$978.00