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	$67.46	7.222%	$72.332	$72.33	$72.35	$72.30
Purchase #2	$203.96	8.772%	$221.8514	$221.85	$221.85	$221.90
Purchase #3	$119.81	6.423%	$127.5054	$127.51	$127.50	$127.50
Purchase #4	$197.31	3.698%	$204.6065	$204.61	$204.60	$204.60
Purchase #5	$164.60	11.848%	$184.1018	$184.10	$184.10	$184.10
Purchase #6	$28.50	7.190%	$30.5492	$30.55	$30.55	$30.50
Purchase #7	$125.72	9.308%	$137.422	$137.42	$137.40	$137.40
7 purchase totals =	$907.36		$978.3683	$978.37	$978.35	$978.30