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	$231.37	4.819%	$242.5197	$242.52	$242.50	$242.50
Purchase #2	$186.86	7.401%	$200.6895	$200.69	$200.70	$200.70
Purchase #3	$74.98	9.821%	$82.3438	$82.34	$82.35	$82.30
Purchase #4	$97.57	12.177%	$109.4511	$109.45	$109.45	$109.50
Purchase #5	$185.64	12.605%	$209.0399	$209.04	$209.05	$209.00
Purchase #6	$219.99	7.256%	$235.9525	$235.95	$235.95	$236.00
Purchase #7	$213.29	9.516%	$233.5867	$233.59	$233.60	$233.60
7 purchase totals =	$1,209.70		$1,313.5832	$1,313.58	$1,313.60	$1,313.60