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	$137.56	9.690%	$150.8896	$150.89	$150.90	$150.90
Purchase #2	$201.41	12.473%	$226.5319	$226.53	$226.55	$226.50
Purchase #3	$156.87	9.790%	$172.2276	$172.23	$172.25	$172.20
Purchase #4	$144.50	4.144%	$150.4881	$150.49	$150.50	$150.50
Purchase #5	$175.27	9.289%	$191.5508	$191.55	$191.55	$191.60
Purchase #6	$221.91	7.854%	$239.3388	$239.34	$239.35	$239.30
Purchase #7	$7.52	12.779%	$8.481	$8.48	$8.50	$8.50
7 purchase totals =	$1,045.04		$1,139.5078	$1,139.51	$1,139.60	$1,139.50