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	$51.27	8.390%	$55.5716	$55.57	$55.55	$55.60
Purchase #2	$11.76	12.497%	$13.2296	$13.23	$13.25	$13.20
Purchase #3	$63.38	10.707%	$70.1661	$70.17	$70.15	$70.20
Purchase #4	$200.76	11.197%	$223.2391	$223.24	$223.25	$223.20
Purchase #5	$226.43	13.409%	$256.792	$256.79	$256.80	$256.80
Purchase #6	$84.30	7.235%	$90.3991	$90.40	$90.40	$90.40
Purchase #7	$5.82	10.170%	$6.4119	$6.41	$6.40	$6.40
7 purchase totals =	$643.72		$715.8094	$715.81	$715.80	$715.80