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	$62.78	12.138%	$70.4002	$70.40	$70.40	$70.40
Purchase #2	$177.98	11.753%	$198.898	$198.90	$198.90	$198.90
Purchase #3	$242.83	11.365%	$270.4276	$270.43	$270.45	$270.40
Purchase #4	$123.90	10.758%	$137.2292	$137.23	$137.25	$137.20
Purchase #5	$176.51	10.154%	$194.4328	$194.43	$194.45	$194.40
Purchase #6	$86.87	11.570%	$96.9209	$96.92	$96.90	$96.90
Purchase #7	$221.96	4.803%	$232.6207	$232.62	$232.60	$232.60
7 purchase totals =	$1,092.83		$1,200.9294	$1,200.93	$1,200.95	$1,200.80