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	$96.44	3.597%	$99.9089	$99.91	$99.90	$99.90
Purchase #2	$250.31	4.659%	$261.9719	$261.97	$261.95	$262.00
Purchase #3	$32.58	11.542%	$36.3404	$36.34	$36.35	$36.30
Purchase #4	$40.94	7.256%	$43.9106	$43.91	$43.90	$43.90
Purchase #5	$106.75	12.397%	$119.9838	$119.98	$120.00	$120.00
Purchase #6	$96.82	6.638%	$103.2469	$103.25	$103.25	$103.20
Purchase #7	$153.59	12.459%	$172.7258	$172.73	$172.75	$172.70
7 purchase totals =	$777.43		$838.0883	$838.09	$838.10	$838.00