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	$6.43	7.554%	$6.9157	$6.92	$6.90	$6.90
Purchase #2	$137.76	10.571%	$152.3226	$152.32	$152.30	$152.30
Purchase #3	$90.68	10.414%	$100.1234	$100.12	$100.10	$100.10
Purchase #4	$140.32	11.542%	$156.5157	$156.52	$156.50	$156.50
Purchase #5	$36.93	10.221%	$40.7046	$40.70	$40.70	$40.70
Purchase #6	$168.36	11.663%	$187.9958	$188.00	$188.00	$188.00
Purchase #7	$213.42	3.680%	$221.2739	$221.27	$221.25	$221.30
7 purchase totals =	$793.90		$865.8517	$865.85	$865.75	$865.80