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	$138.59	6.426%	$147.4958	$147.50	$147.50	$147.50
Purchase #2	$127.40	3.127%	$131.3838	$131.38	$131.40	$131.40
Purchase #3	$123.36	5.132%	$129.6908	$129.69	$129.70	$129.70
Purchase #4	$161.51	12.820%	$182.2156	$182.22	$182.20	$182.20
Purchase #5	$69.29	3.825%	$71.9403	$71.94	$71.95	$71.90
Purchase #6	$136.41	13.331%	$154.5948	$154.59	$154.60	$154.60
Purchase #7	$242.76	9.676%	$266.2495	$266.25	$266.25	$266.20
7 purchase totals =	$999.32		$1,083.5706	$1,083.57	$1,083.60	$1,083.50