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	$5.60	11.305%	$6.2331	$6.23	$6.25	$6.20
Purchase #2	$134.57	4.128%	$140.125	$140.13	$140.15	$140.10
Purchase #3	$231.71	10.770%	$256.6652	$256.67	$256.65	$256.70
Purchase #4	$240.83	13.582%	$273.5395	$273.54	$273.55	$273.50
Purchase #5	$101.77	10.333%	$112.2859	$112.29	$112.30	$112.30
Purchase #6	$147.79	5.496%	$155.9125	$155.91	$155.90	$155.90
Purchase #7	$163.29	13.471%	$185.2868	$185.29	$185.30	$185.30
7 purchase totals =	$1,025.56		$1,130.0480	$1,130.06	$1,130.10	$1,130.00