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	$115.53	9.777%	$126.8254	$126.83	$126.85	$126.80
Purchase #2	$119.94	11.174%	$133.3421	$133.34	$133.35	$133.30
Purchase #3	$169.83	9.266%	$185.5664	$185.57	$185.55	$185.60
Purchase #4	$46.78	11.620%	$52.2158	$52.22	$52.20	$52.20
Purchase #5	$174.46	6.233%	$185.3341	$185.33	$185.35	$185.30
Purchase #6	$35.51	7.575%	$38.1999	$38.20	$38.20	$38.20
Purchase #7	$219.97	13.832%	$250.3963	$250.40	$250.40	$250.40
7 purchase totals =	$882.02		$971.8800	$971.89	$971.90	$971.80