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	$156.58	12.651%	$176.3889	$176.39	$176.40	$176.40
Purchase #2	$250.36	9.798%	$274.8903	$274.89	$274.90	$274.90
Purchase #3	$247.40	9.277%	$270.3513	$270.35	$270.35	$270.40
Purchase #4	$89.98	6.640%	$95.9547	$95.95	$95.95	$96.00
Purchase #5	$30.88	9.360%	$33.7704	$33.77	$33.75	$33.80
Purchase #6	$213.57	5.722%	$225.7905	$225.79	$225.80	$225.80
Purchase #7	$171.25	4.386%	$178.761	$178.76	$178.75	$178.80
7 purchase totals =	$1,160.02		$1,255.9071	$1,255.90	$1,255.90	$1,256.10