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	$101.57	12.552%	$114.3191	$114.32	$114.30	$114.30
Purchase #2	$51.75	7.687%	$55.728	$55.73	$55.75	$55.70
Purchase #3	$105.95	10.291%	$116.8533	$116.85	$116.85	$116.90
Purchase #4	$54.71	13.211%	$61.9377	$61.94	$61.95	$61.90
Purchase #5	$38.49	4.179%	$40.0985	$40.10	$40.10	$40.10
Purchase #6	$241.87	13.414%	$274.3144	$274.31	$274.30	$274.30
Purchase #7	$105.98	11.217%	$117.8678	$117.87	$117.85	$117.90
7 purchase totals =	$700.32		$781.1188	$781.12	$781.10	$781.10