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	$36.27	11.514%	$40.4461	$40.45	$40.45	$40.40
Purchase #2	$6.95	6.125%	$7.3757	$7.38	$7.40	$7.40
Purchase #3	$124.73	12.187%	$139.9308	$139.93	$139.95	$139.90
Purchase #4	$101.37	7.629%	$109.1035	$109.10	$109.10	$109.10
Purchase #5	$159.69	7.796%	$172.1394	$172.14	$172.15	$172.10
Purchase #6	$76.95	12.200%	$86.3379	$86.34	$86.35	$86.30
Purchase #7	$47.76	7.405%	$51.2966	$51.30	$51.30	$51.30
7 purchase totals =	$553.72		$606.6300	$606.64	$606.70	$606.50