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	$150.88	13.655%	$171.4827	$171.48	$171.50	$171.50
Purchase #2	$43.48	8.375%	$47.1215	$47.12	$47.10	$47.10
Purchase #3	$179.86	13.174%	$203.5548	$203.55	$203.55	$203.60
Purchase #4	$112.69	13.184%	$127.547	$127.55	$127.55	$127.50
Purchase #5	$224.26	8.608%	$243.5643	$243.56	$243.55	$243.60
Purchase #6	$66.48	9.146%	$72.5603	$72.56	$72.55	$72.60
Purchase #7	$201.83	10.491%	$223.004	$223.00	$223.00	$223.00
7 purchase totals =	$979.48		$1,088.8346	$1,088.82	$1,088.80	$1,088.90