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	$121.68	12.808%	$137.2648	$137.26	$137.25	$137.30
Purchase #2	$179.35	3.220%	$185.1251	$185.13	$185.15	$185.10
Purchase #3	$163.30	11.360%	$181.8509	$181.85	$181.85	$181.90
Purchase #4	$110.59	10.872%	$122.6133	$122.61	$122.60	$122.60
Purchase #5	$181.46	7.748%	$195.5195	$195.52	$195.50	$195.50
Purchase #6	$218.44	5.238%	$229.8819	$229.88	$229.90	$229.90
Purchase #7	$28.42	11.219%	$31.6084	$31.61	$31.60	$31.60
7 purchase totals =	$1,003.24		$1,083.8639	$1,083.86	$1,083.85	$1,083.90