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	$140.40	3.192%	$144.8816	$144.88	$144.90	$144.90
Purchase #2	$64.97	9.129%	$70.9011	$70.90	$70.90	$70.90
Purchase #3	$110.71	6.172%	$117.543	$117.54	$117.55	$117.50
Purchase #4	$92.42	10.772%	$102.3755	$102.38	$102.40	$102.40
Purchase #5	$74.94	7.513%	$80.5702	$80.57	$80.55	$80.60
Purchase #6	$57.90	3.469%	$59.9086	$59.91	$59.90	$59.90
Purchase #7	$243.54	9.284%	$266.1503	$266.15	$266.15	$266.20
7 purchase totals =	$784.88		$842.3303	$842.33	$842.35	$842.40