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	$56.47	8.645%	$61.3518	$61.35	$61.35	$61.40
Purchase #2	$66.58	12.835%	$75.1255	$75.13	$75.15	$75.10
Purchase #3	$137.91	3.855%	$143.2264	$143.23	$143.25	$143.20
Purchase #4	$52.76	13.568%	$59.9185	$59.92	$59.90	$59.90
Purchase #5	$141.41	8.336%	$153.1979	$153.20	$153.20	$153.20
Purchase #6	$82.38	9.796%	$90.4499	$90.45	$90.45	$90.40
Purchase #7	$210.49	3.212%	$217.2509	$217.25	$217.25	$217.30
7 purchase totals =	$748.00		$800.5209	$800.53	$800.55	$800.50