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	$105.57	3.442%	$109.2037	$109.20	$109.20	$109.20
Purchase #2	$63.48	12.572%	$71.4607	$71.46	$71.45	$71.50
Purchase #3	$92.50	12.837%	$104.3742	$104.37	$104.35	$104.40
Purchase #4	$215.83	10.563%	$238.6281	$238.63	$238.65	$238.60
Purchase #5	$208.49	9.140%	$227.546	$227.55	$227.55	$227.50
Purchase #6	$230.46	4.555%	$240.9575	$240.96	$240.95	$241.00
Purchase #7	$46.69	7.752%	$50.3094	$50.31	$50.30	$50.30
7 purchase totals =	$963.02		$1,042.4796	$1,042.48	$1,042.45	$1,042.50