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	$250.25	5.587%	$264.2315	$264.23	$264.25	$264.20
Purchase #2	$239.72	10.218%	$264.2146	$264.21	$264.20	$264.20
Purchase #3	$31.48	9.592%	$34.4996	$34.50	$34.50	$34.50
Purchase #4	$104.87	12.390%	$117.8634	$117.86	$117.85	$117.90
Purchase #5	$196.64	12.421%	$221.0647	$221.06	$221.05	$221.10
Purchase #6	$43.37	4.379%	$45.2692	$45.27	$45.25	$45.30
Purchase #7	$184.45	10.111%	$203.0997	$203.10	$203.10	$203.10
7 purchase totals =	$1,050.78		$1,150.2427	$1,150.23	$1,150.20	$1,150.30