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	$100.25	3.253%	$103.5111	$103.51	$103.50	$103.50
Purchase #2	$240.67	7.436%	$258.5662	$258.57	$258.55	$258.60
Purchase #3	$10.86	8.629%	$11.7971	$11.80	$11.80	$11.80
Purchase #4	$234.61	6.787%	$250.533	$250.53	$250.55	$250.50
Purchase #5	$244.46	10.761%	$270.7663	$270.77	$270.75	$270.80
Purchase #6	$210.73	12.171%	$236.3779	$236.38	$236.40	$236.40
Purchase #7	$70.72	9.338%	$77.3238	$77.32	$77.30	$77.30
7 purchase totals =	$1,112.30		$1,208.8754	$1,208.88	$1,208.85	$1,208.90