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	$72.76	11.262%	$80.9542	$80.95	$80.95	$81.00
Purchase #2	$110.71	11.386%	$123.3154	$123.32	$123.30	$123.30
Purchase #3	$76.55	4.379%	$79.9021	$79.90	$79.90	$79.90
Purchase #4	$35.72	13.747%	$40.6304	$40.63	$40.65	$40.60
Purchase #5	$11.33	6.208%	$12.0334	$12.03	$12.05	$12.00
Purchase #6	$43.69	11.419%	$48.679	$48.68	$48.70	$48.70
Purchase #7	$153.79	9.414%	$168.2678	$168.27	$168.25	$168.30
7 purchase totals =	$504.55		$553.7823	$553.78	$553.80	$553.80