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	$79.88	3.225%	$82.4561	$82.46	$82.45	$82.50
Purchase #2	$117.65	5.763%	$124.4302	$124.43	$124.45	$124.40
Purchase #3	$245.31	4.121%	$255.4192	$255.42	$255.40	$255.40
Purchase #4	$178.95	9.803%	$196.4925	$196.49	$196.50	$196.50
Purchase #5	$229.47	12.170%	$257.3965	$257.40	$257.40	$257.40
Purchase #6	$243.61	7.423%	$261.6932	$261.69	$261.70	$261.70
Purchase #7	$57.68	12.520%	$64.9015	$64.90	$64.90	$64.90
7 purchase totals =	$1,152.55		$1,242.7892	$1,242.79	$1,242.80	$1,242.80