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	$133.50	10.770%	$147.878	$147.88	$147.90	$147.90
Purchase #2	$184.73	4.826%	$193.6451	$193.65	$193.65	$193.60
Purchase #3	$53.42	7.561%	$57.4591	$57.46	$57.45	$57.50
Purchase #4	$121.53	12.228%	$136.3907	$136.39	$136.40	$136.40
Purchase #5	$80.71	6.140%	$85.6656	$85.67	$85.65	$85.70
Purchase #6	$42.31	6.762%	$45.171	$45.17	$45.15	$45.20
Purchase #7	$145.88	5.686%	$154.1747	$154.17	$154.15	$154.20
7 purchase totals =	$762.08		$820.3842	$820.39	$820.35	$820.50