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	$107.70	7.521%	$115.8001	$115.80	$115.80	$115.80
Purchase #2	$108.80	13.304%	$123.2748	$123.27	$123.25	$123.30
Purchase #3	$41.80	9.785%	$45.8901	$45.89	$45.90	$45.90
Purchase #4	$187.78	6.614%	$200.1998	$200.20	$200.20	$200.20
Purchase #5	$147.60	6.270%	$156.8545	$156.85	$156.85	$156.90
Purchase #6	$16.77	12.711%	$18.9016	$18.90	$18.90	$18.90
Purchase #7	$149.97	3.353%	$154.9985	$155.00	$155.00	$155.00
7 purchase totals =	$760.42		$815.9194	$815.91	$815.90	$816.00