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	$220.65	11.126%	$245.1995	$245.20	$245.20	$245.20
Purchase #2	$152.36	8.804%	$165.7738	$165.77	$165.75	$165.80
Purchase #3	$102.42	3.855%	$106.3683	$106.37	$106.35	$106.40
Purchase #4	$100.33	5.742%	$106.0909	$106.09	$106.10	$106.10
Purchase #5	$133.68	12.649%	$150.5892	$150.59	$150.60	$150.60
Purchase #6	$52.52	12.770%	$59.2268	$59.23	$59.25	$59.20
Purchase #7	$82.96	10.470%	$91.6459	$91.65	$91.65	$91.60
7 purchase totals =	$844.92		$924.8944	$924.90	$924.90	$924.90