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	$248.98	13.618%	$282.8861	$282.89	$282.90	$282.90
Purchase #2	$98.82	10.795%	$109.4876	$109.49	$109.50	$109.50
Purchase #3	$164.39	12.444%	$184.8467	$184.85	$184.85	$184.80
Purchase #4	$30.91	7.645%	$33.2731	$33.27	$33.25	$33.30
Purchase #5	$6.76	10.557%	$7.4737	$7.47	$7.45	$7.50
Purchase #6	$141.50	11.369%	$157.5871	$157.59	$157.60	$157.60
Purchase #7	$43.37	7.531%	$46.6362	$46.64	$46.65	$46.60
7 purchase totals =	$734.73		$822.1905	$822.20	$822.20	$822.20