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	$100.78	10.595%	$111.4576	$111.46	$111.45	$111.50
Purchase #2	$158.76	10.154%	$174.8805	$174.88	$174.90	$174.90
Purchase #3	$200.37	4.781%	$209.9497	$209.95	$209.95	$209.90
Purchase #4	$41.89	13.755%	$47.652	$47.65	$47.65	$47.70
Purchase #5	$6.88	9.551%	$7.5371	$7.54	$7.55	$7.50
Purchase #6	$224.48	10.444%	$247.9247	$247.92	$247.90	$247.90
Purchase #7	$54.36	12.579%	$61.1979	$61.20	$61.20	$61.20
7 purchase totals =	$787.52		$860.5995	$860.60	$860.60	$860.60