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	$246.69	7.339%	$264.7946	$264.79	$264.80	$264.80
Purchase #2	$119.64	9.597%	$131.1219	$131.12	$131.10	$131.10
Purchase #3	$209.46	12.590%	$235.831	$235.83	$235.85	$235.80
Purchase #4	$238.94	11.307%	$265.9569	$265.96	$265.95	$266.00
Purchase #5	$202.82	3.372%	$209.6591	$209.66	$209.65	$209.70
Purchase #6	$160.78	6.651%	$171.4735	$171.47	$171.45	$171.50
Purchase #7	$56.90	8.274%	$61.6079	$61.61	$61.60	$61.60
7 purchase totals =	$1,235.23		$1,340.4449	$1,340.44	$1,340.40	$1,340.50