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	$72.59	13.651%	$82.4993	$82.50	$82.50	$82.50
Purchase #2	$115.65	10.436%	$127.7192	$127.72	$127.70	$127.70
Purchase #3	$126.30	5.417%	$133.1417	$133.14	$133.15	$133.10
Purchase #4	$223.39	7.590%	$240.3453	$240.35	$240.35	$240.30
Purchase #5	$168.25	9.653%	$184.4912	$184.49	$184.50	$184.50
Purchase #6	$84.47	13.826%	$96.1488	$96.15	$96.15	$96.10
Purchase #7	$30.62	8.209%	$33.1336	$33.13	$33.15	$33.10
7 purchase totals =	$821.27		$897.4791	$897.48	$897.50	$897.30