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	$64.36	11.142%	$71.531	$71.53	$71.55	$71.50
Purchase #2	$137.55	4.688%	$143.9983	$144.00	$144.00	$144.00
Purchase #3	$143.85	12.861%	$162.3505	$162.35	$162.35	$162.40
Purchase #4	$224.95	4.279%	$234.5756	$234.58	$234.60	$234.60
Purchase #5	$126.81	3.629%	$131.4119	$131.41	$131.40	$131.40
Purchase #6	$167.85	13.116%	$189.8652	$189.87	$189.85	$189.90
Purchase #7	$220.63	12.575%	$248.3742	$248.37	$248.35	$248.40
7 purchase totals =	$1,086.00		$1,182.1067	$1,182.11	$1,182.10	$1,182.20