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	$70.48	11.815%	$78.8072	$78.81	$78.80	$78.80
Purchase #2	$181.62	12.450%	$204.2317	$204.23	$204.25	$204.20
Purchase #3	$203.34	5.706%	$214.9426	$214.94	$214.95	$214.90
Purchase #4	$181.61	3.161%	$187.3507	$187.35	$187.35	$187.40
Purchase #5	$159.47	5.447%	$168.1563	$168.16	$168.15	$168.20
Purchase #6	$33.39	11.394%	$37.1945	$37.19	$37.20	$37.20
Purchase #7	$80.47	3.756%	$83.4925	$83.49	$83.50	$83.50
7 purchase totals =	$910.38		$974.1755	$974.17	$974.20	$974.20