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	$227.60	9.729%	$249.7432	$249.74	$249.75	$249.70
Purchase #2	$77.38	6.210%	$82.1853	$82.19	$82.20	$82.20
Purchase #3	$180.85	12.772%	$203.9482	$203.95	$203.95	$203.90
Purchase #4	$176.47	3.623%	$182.8635	$182.86	$182.85	$182.90
Purchase #5	$216.50	12.524%	$243.6145	$243.61	$243.60	$243.60
Purchase #6	$173.61	6.803%	$185.4207	$185.42	$185.40	$185.40
Purchase #7	$177.59	4.709%	$185.9527	$185.95	$185.95	$186.00
7 purchase totals =	$1,230.00		$1,333.7281	$1,333.72	$1,333.70	$1,333.70