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	$31.60	10.285%	$34.8501	$34.85	$34.85	$34.90
Purchase #2	$165.75	3.315%	$171.2446	$171.24	$171.25	$171.20
Purchase #3	$232.81	8.744%	$253.1669	$253.17	$253.15	$253.20
Purchase #4	$231.30	3.301%	$238.9352	$238.94	$238.95	$238.90
Purchase #5	$83.26	7.127%	$89.1939	$89.19	$89.20	$89.20
Purchase #6	$216.32	10.175%	$238.3306	$238.33	$238.35	$238.30
Purchase #7	$29.64	13.457%	$33.6287	$33.63	$33.65	$33.60
7 purchase totals =	$990.68		$1,059.3500	$1,059.35	$1,059.40	$1,059.30