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	$127.34	12.490%	$143.2448	$143.24	$143.25	$143.20
Purchase #2	$154.55	8.550%	$167.764	$167.76	$167.75	$167.80
Purchase #3	$197.80	13.860%	$225.2151	$225.22	$225.20	$225.20
Purchase #4	$179.50	9.732%	$196.9689	$196.97	$196.95	$197.00
Purchase #5	$179.54	6.306%	$190.8618	$190.86	$190.85	$190.90
Purchase #6	$98.40	11.695%	$109.9079	$109.91	$109.90	$109.90
Purchase #7	$38.58	8.797%	$41.9739	$41.97	$41.95	$42.00
7 purchase totals =	$975.71		$1,075.9364	$1,075.93	$1,075.85	$1,076.00