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	$135.55	12.675%	$152.731	$152.73	$152.75	$152.70
Purchase #2	$133.86	10.520%	$147.9421	$147.94	$147.95	$147.90
Purchase #3	$108.71	7.521%	$116.8861	$116.89	$116.90	$116.90
Purchase #4	$22.39	3.839%	$23.2496	$23.25	$23.25	$23.20
Purchase #5	$51.81	11.219%	$57.6226	$57.62	$57.60	$57.60
Purchase #6	$126.50	13.449%	$143.513	$143.51	$143.50	$143.50
Purchase #7	$132.36	7.385%	$142.1348	$142.13	$142.15	$142.10
7 purchase totals =	$711.18		$784.0792	$784.07	$784.10	$783.90