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	$132.56	5.618%	$140.0072	$140.01	$140.00	$140.00
Purchase #2	$73.64	6.544%	$78.459	$78.46	$78.45	$78.50
Purchase #3	$203.70	6.324%	$216.582	$216.58	$216.60	$216.60
Purchase #4	$117.34	12.178%	$131.6297	$131.63	$131.65	$131.60
Purchase #5	$207.67	5.571%	$219.2393	$219.24	$219.25	$219.20
Purchase #6	$14.81	7.274%	$15.8873	$15.89	$15.90	$15.90
Purchase #7	$87.37	13.830%	$99.4533	$99.45	$99.45	$99.50
7 purchase totals =	$837.09		$901.2578	$901.26	$901.30	$901.30