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	$225.34	6.362%	$239.6761	$239.68	$239.70	$239.70
Purchase #2	$59.32	10.601%	$65.6085	$65.61	$65.60	$65.60
Purchase #3	$222.42	5.140%	$233.8524	$233.85	$233.85	$233.90
Purchase #4	$186.92	10.132%	$205.8587	$205.86	$205.85	$205.90
Purchase #5	$213.88	9.583%	$234.3761	$234.38	$234.40	$234.40
Purchase #6	$117.33	7.148%	$125.7167	$125.72	$125.70	$125.70
Purchase #7	$43.30	7.107%	$46.3773	$46.38	$46.40	$46.40
7 purchase totals =	$1,068.51		$1,151.4658	$1,151.48	$1,151.50	$1,151.60