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	$163.37	4.858%	$171.3065	$171.31	$171.30	$171.30
Purchase #2	$240.56	13.597%	$273.2689	$273.27	$273.25	$273.30
Purchase #3	$236.38	8.262%	$255.9097	$255.91	$255.90	$255.90
Purchase #4	$56.42	8.667%	$61.3099	$61.31	$61.30	$61.30
Purchase #5	$129.66	5.173%	$136.3673	$136.37	$136.35	$136.40
Purchase #6	$87.75	9.715%	$96.2749	$96.27	$96.25	$96.30
Purchase #7	$203.39	10.543%	$224.8334	$224.83	$224.85	$224.80
7 purchase totals =	$1,117.53		$1,219.2706	$1,219.27	$1,219.20	$1,219.30