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	$172.89	5.801%	$182.9193	$182.92	$182.90	$182.90
Purchase #2	$200.44	10.672%	$221.831	$221.83	$221.85	$221.80
Purchase #3	$10.35	11.529%	$11.5433	$11.54	$11.55	$11.50
Purchase #4	$182.62	7.127%	$195.6353	$195.64	$195.65	$195.60
Purchase #5	$37.68	6.677%	$40.1959	$40.20	$40.20	$40.20
Purchase #6	$140.30	11.547%	$156.5004	$156.50	$156.50	$156.50
Purchase #7	$119.92	9.472%	$131.2788	$131.28	$131.30	$131.30
7 purchase totals =	$864.20		$939.9040	$939.91	$939.95	$939.80