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	$172.47	9.838%	$189.4376	$189.44	$189.45	$189.40
Purchase #2	$64.48	12.856%	$72.7695	$72.77	$72.75	$72.80
Purchase #3	$75.54	6.570%	$80.503	$80.50	$80.50	$80.50
Purchase #4	$162.36	5.766%	$171.7217	$171.72	$171.70	$171.70
Purchase #5	$167.86	10.391%	$185.3023	$185.30	$185.30	$185.30
Purchase #6	$32.37	12.640%	$36.4616	$36.46	$36.45	$36.50
Purchase #7	$250.39	7.172%	$268.348	$268.35	$268.35	$268.30
7 purchase totals =	$925.47		$1,004.5437	$1,004.54	$1,004.50	$1,004.50