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	$79.96	4.341%	$83.4311	$83.43	$83.45	$83.40
Purchase #2	$54.63	6.673%	$58.2755	$58.28	$58.30	$58.30
Purchase #3	$24.37	12.843%	$27.4998	$27.50	$27.50	$27.50
Purchase #4	$150.33	3.432%	$155.4893	$155.49	$155.50	$155.50
Purchase #5	$128.27	3.581%	$132.8633	$132.86	$132.85	$132.90
Purchase #6	$80.32	10.235%	$88.5408	$88.54	$88.55	$88.50
Purchase #7	$57.39	7.268%	$61.5611	$61.56	$61.55	$61.60
7 purchase totals =	$575.27		$607.6609	$607.66	$607.70	$607.70