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	$57.53	12.341%	$64.6298	$64.63	$64.65	$64.60
Purchase #2	$176.97	3.132%	$182.5127	$182.51	$182.50	$182.50
Purchase #3	$115.25	7.475%	$123.8649	$123.86	$123.85	$123.90
Purchase #4	$42.26	9.588%	$46.3119	$46.31	$46.30	$46.30
Purchase #5	$167.30	10.867%	$185.4805	$185.48	$185.50	$185.50
Purchase #6	$33.63	7.717%	$36.2252	$36.23	$36.25	$36.20
Purchase #7	$37.80	10.303%	$41.6945	$41.69	$41.70	$41.70
7 purchase totals =	$630.74		$680.7195	$680.71	$680.75	$680.70