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	$83.43	8.540%	$90.5549	$90.55	$90.55	$90.60
Purchase #2	$117.76	9.652%	$129.1262	$129.13	$129.15	$129.10
Purchase #3	$250.27	9.436%	$273.8855	$273.89	$273.90	$273.90
Purchase #4	$114.48	3.577%	$118.5749	$118.57	$118.55	$118.60
Purchase #5	$84.91	7.553%	$91.3233	$91.32	$91.30	$91.30
Purchase #6	$105.27	12.503%	$118.4319	$118.43	$118.45	$118.40
Purchase #7	$217.84	5.789%	$230.4508	$230.45	$230.45	$230.50
7 purchase totals =	$973.96		$1,052.3475	$1,052.34	$1,052.35	$1,052.40