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	$247.32	13.383%	$280.4188	$280.42	$280.40	$280.40
Purchase #2	$141.63	10.802%	$156.9289	$156.93	$156.95	$156.90
Purchase #3	$154.39	12.221%	$173.258	$173.26	$173.25	$173.30
Purchase #4	$141.45	10.518%	$156.3277	$156.33	$156.35	$156.30
Purchase #5	$157.82	12.122%	$176.9509	$176.95	$176.95	$177.00
Purchase #6	$130.95	5.312%	$137.9061	$137.91	$137.90	$137.90
Purchase #7	$182.79	7.398%	$196.3128	$196.31	$196.30	$196.30
7 purchase totals =	$1,156.35		$1,278.1032	$1,278.11	$1,278.10	$1,278.10