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	$129.53	10.658%	$143.3353	$143.34	$143.35	$143.30
Purchase #2	$112.98	6.511%	$120.3361	$120.34	$120.35	$120.30
Purchase #3	$55.51	9.725%	$60.9083	$60.91	$60.90	$60.90
Purchase #4	$83.63	7.445%	$89.8563	$89.86	$89.85	$89.90
Purchase #5	$72.33	10.781%	$80.1279	$80.13	$80.15	$80.10
Purchase #6	$140.60	8.252%	$152.2023	$152.20	$152.20	$152.20
Purchase #7	$38.39	8.198%	$41.5372	$41.54	$41.55	$41.50
7 purchase totals =	$632.97		$688.3034	$688.32	$688.35	$688.20