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	$19.49	7.262%	$20.9054	$20.91	$20.90	$20.90
Purchase #2	$205.49	13.796%	$233.8394	$233.84	$233.85	$233.80
Purchase #3	$159.35	9.765%	$174.9105	$174.91	$174.90	$174.90
Purchase #4	$86.55	13.238%	$98.0075	$98.01	$98.00	$98.00
Purchase #5	$124.36	12.660%	$140.104	$140.10	$140.10	$140.10
Purchase #6	$11.98	10.504%	$13.2384	$13.24	$13.25	$13.20
Purchase #7	$38.86	9.424%	$42.5222	$42.52	$42.50	$42.50
7 purchase totals =	$646.08		$723.5274	$723.53	$723.50	$723.40