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	$38.32	11.662%	$42.7889	$42.79	$42.80	$42.80
Purchase #2	$31.25	12.324%	$35.1013	$35.10	$35.10	$35.10
Purchase #3	$173.33	9.127%	$189.1498	$189.15	$189.15	$189.10
Purchase #4	$162.97	6.136%	$172.9698	$172.97	$172.95	$173.00
Purchase #5	$117.76	12.580%	$132.5742	$132.57	$132.55	$132.60
Purchase #6	$140.96	10.821%	$156.2133	$156.21	$156.20	$156.20
Purchase #7	$106.86	11.869%	$119.5432	$119.54	$119.55	$119.50
7 purchase totals =	$771.45		$848.3405	$848.33	$848.30	$848.30