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	$135.98	3.140%	$140.2498	$140.25	$140.25	$140.20
Purchase #2	$224.76	8.430%	$243.7073	$243.71	$243.70	$243.70
Purchase #3	$46.32	13.311%	$52.4857	$52.49	$52.50	$52.50
Purchase #4	$215.72	11.547%	$240.6292	$240.63	$240.65	$240.60
Purchase #5	$160.89	6.853%	$171.9158	$171.92	$171.90	$171.90
Purchase #6	$104.33	6.718%	$111.3389	$111.34	$111.35	$111.30
Purchase #7	$158.51	11.595%	$176.8892	$176.89	$176.90	$176.90
7 purchase totals =	$1,046.51		$1,137.2159	$1,137.23	$1,137.25	$1,137.10