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	$69.75	12.734%	$78.632	$78.63	$78.65	$78.60
Purchase #2	$156.25	5.163%	$164.3172	$164.32	$164.30	$164.30
Purchase #3	$36.29	12.249%	$40.7352	$40.74	$40.75	$40.70
Purchase #4	$242.34	7.752%	$261.1262	$261.13	$261.15	$261.10
Purchase #5	$78.29	9.372%	$85.6273	$85.63	$85.65	$85.60
Purchase #6	$149.36	4.807%	$156.5397	$156.54	$156.55	$156.50
Purchase #7	$147.68	11.702%	$164.9615	$164.96	$164.95	$165.00
7 purchase totals =	$879.96		$951.9391	$951.95	$952.00	$951.80