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	$28.59	10.334%	$31.5445	$31.54	$31.55	$31.50
Purchase #2	$195.41	9.460%	$213.8958	$213.90	$213.90	$213.90
Purchase #3	$210.84	8.828%	$229.453	$229.45	$229.45	$229.50
Purchase #4	$185.38	5.865%	$196.2525	$196.25	$196.25	$196.30
Purchase #5	$211.85	10.244%	$233.5519	$233.55	$233.55	$233.60
Purchase #6	$197.75	13.550%	$224.5451	$224.55	$224.55	$224.50
Purchase #7	$200.41	13.340%	$227.1447	$227.14	$227.15	$227.10
7 purchase totals =	$1,230.23		$1,356.3875	$1,356.38	$1,356.40	$1,356.40