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	$221.64	12.811%	$250.0343	$250.03	$250.05	$250.00
Purchase #2	$197.78	9.634%	$216.8341	$216.83	$216.85	$216.80
Purchase #3	$242.50	5.411%	$255.6217	$255.62	$255.60	$255.60
Purchase #4	$162.35	7.572%	$174.6431	$174.64	$174.65	$174.60
Purchase #5	$34.39	11.761%	$38.4346	$38.43	$38.45	$38.40
Purchase #6	$32.60	13.558%	$37.0199	$37.02	$37.00	$37.00
Purchase #7	$106.96	11.687%	$119.4604	$119.46	$119.45	$119.50
7 purchase totals =	$998.22		$1,092.0481	$1,092.03	$1,092.05	$1,091.90