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	$76.86	12.208%	$86.2431	$86.24	$86.25	$86.20
Purchase #2	$180.96	10.655%	$200.2413	$200.24	$200.25	$200.20
Purchase #3	$160.86	13.265%	$182.1981	$182.20	$182.20	$182.20
Purchase #4	$69.48	12.728%	$78.3234	$78.32	$78.30	$78.30
Purchase #5	$46.91	5.525%	$49.5018	$49.50	$49.50	$49.50
Purchase #6	$63.68	5.443%	$67.1461	$67.15	$67.15	$67.10
Purchase #7	$181.74	12.567%	$204.5793	$204.58	$204.60	$204.60
7 purchase totals =	$780.49		$868.2331	$868.23	$868.25	$868.10