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	$76.35	3.349%	$78.907	$78.91	$78.90	$78.90
Purchase #2	$201.64	11.501%	$224.8306	$224.83	$224.85	$224.80
Purchase #3	$39.38	3.405%	$40.7209	$40.72	$40.70	$40.70
Purchase #4	$170.69	8.649%	$185.453	$185.45	$185.45	$185.50
Purchase #5	$210.82	13.729%	$239.7635	$239.76	$239.75	$239.80
Purchase #6	$99.71	11.229%	$110.9064	$110.91	$110.90	$110.90
Purchase #7	$75.66	3.275%	$78.1379	$78.14	$78.15	$78.10
7 purchase totals =	$874.25		$958.7193	$958.72	$958.70	$958.70