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	$55.29	3.145%	$57.0289	$57.03	$57.05	$57.00
Purchase #2	$208.37	11.622%	$232.5868	$232.59	$232.60	$232.60
Purchase #3	$61.95	7.427%	$66.551	$66.55	$66.55	$66.60
Purchase #4	$90.41	7.484%	$97.1763	$97.18	$97.20	$97.20
Purchase #5	$229.89	7.287%	$246.6421	$246.64	$246.65	$246.60
Purchase #6	$179.64	3.225%	$185.4334	$185.43	$185.45	$185.40
Purchase #7	$80.82	10.164%	$89.0345	$89.03	$89.05	$89.00
7 purchase totals =	$906.37		$974.4530	$974.45	$974.55	$974.40