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	$102.34	7.391%	$109.9039	$109.90	$109.90	$109.90
Purchase #2	$147.67	12.582%	$166.2498	$166.25	$166.25	$166.20
Purchase #3	$38.39	8.243%	$41.5545	$41.55	$41.55	$41.60
Purchase #4	$98.79	8.648%	$107.3334	$107.33	$107.35	$107.30
Purchase #5	$37.69	13.517%	$42.7846	$42.78	$42.80	$42.80
Purchase #6	$208.35	7.612%	$224.2096	$224.21	$224.20	$224.20
Purchase #7	$99.63	4.167%	$103.7816	$103.78	$103.80	$103.80
7 purchase totals =	$732.86		$795.8174	$795.80	$795.85	$795.80