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	$137.55	11.562%	$153.4535	$153.45	$153.45	$153.50
Purchase #2	$29.75	12.294%	$33.4075	$33.41	$33.40	$33.40
Purchase #3	$100.42	13.554%	$114.0309	$114.03	$114.05	$114.00
Purchase #4	$245.27	12.401%	$275.6859	$275.69	$275.70	$275.70
Purchase #5	$58.54	9.846%	$64.3038	$64.30	$64.30	$64.30
Purchase #6	$250.85	8.856%	$273.0653	$273.07	$273.05	$273.10
Purchase #7	$163.50	10.311%	$180.3585	$180.36	$180.35	$180.40
7 purchase totals =	$985.88		$1,094.3054	$1,094.31	$1,094.30	$1,094.40