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	$13.76	11.193%	$15.3002	$15.30	$15.30	$15.30
Purchase #2	$63.88	12.812%	$72.0643	$72.06	$72.05	$72.10
Purchase #3	$70.30	11.171%	$78.1532	$78.15	$78.15	$78.20
Purchase #4	$177.58	8.523%	$192.7151	$192.72	$192.70	$192.70
Purchase #5	$132.77	7.637%	$142.9096	$142.91	$142.90	$142.90
Purchase #6	$120.82	13.483%	$137.1102	$137.11	$137.10	$137.10
Purchase #7	$245.80	11.333%	$273.6565	$273.66	$273.65	$273.70
7 purchase totals =	$824.91		$911.9091	$911.91	$911.85	$912.00