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	$202.44	12.651%	$228.0507	$228.05	$228.05	$228.10
Purchase #2	$238.61	7.700%	$256.983	$256.98	$257.00	$257.00
Purchase #3	$123.72	7.470%	$132.9619	$132.96	$132.95	$133.00
Purchase #4	$18.62	8.766%	$20.2522	$20.25	$20.25	$20.30
Purchase #5	$94.72	5.336%	$99.7743	$99.77	$99.75	$99.80
Purchase #6	$36.45	10.731%	$40.3614	$40.36	$40.35	$40.40
Purchase #7	$11.44	12.629%	$12.8848	$12.88	$12.90	$12.90
7 purchase totals =	$726.00		$791.2683	$791.25	$791.25	$791.50