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	$137.32	3.512%	$142.1427	$142.14	$142.15	$142.10
Purchase #2	$132.82	8.665%	$144.3289	$144.33	$144.35	$144.30
Purchase #3	$74.41	5.557%	$78.545	$78.55	$78.55	$78.50
Purchase #4	$150.71	11.695%	$168.3355	$168.34	$168.35	$168.30
Purchase #5	$32.33	8.315%	$35.0182	$35.02	$35.00	$35.00
Purchase #6	$189.93	10.739%	$210.3266	$210.33	$210.35	$210.30
Purchase #7	$201.52	4.309%	$210.2035	$210.20	$210.20	$210.20
7 purchase totals =	$919.04		$988.9004	$988.91	$988.95	$988.70