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	$43.95	12.317%	$49.3633	$49.36	$49.35	$49.40
Purchase #2	$148.28	10.755%	$164.2275	$164.23	$164.25	$164.20
Purchase #3	$152.90	10.157%	$168.4301	$168.43	$168.45	$168.40
Purchase #4	$146.89	12.264%	$164.9046	$164.90	$164.90	$164.90
Purchase #5	$121.83	7.861%	$131.4071	$131.41	$131.40	$131.40
Purchase #6	$17.69	12.633%	$19.9248	$19.92	$19.90	$19.90
Purchase #7	$170.66	12.391%	$191.8065	$191.81	$191.80	$191.80
7 purchase totals =	$802.20		$890.0639	$890.06	$890.05	$890.00