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	$109.43	12.429%	$123.0311	$123.03	$123.05	$123.00
Purchase #2	$174.74	5.562%	$184.459	$184.46	$184.45	$184.50
Purchase #3	$154.45	12.802%	$174.2227	$174.22	$174.20	$174.20
Purchase #4	$36.39	7.825%	$39.2375	$39.24	$39.25	$39.20
Purchase #5	$22.57	11.233%	$25.1053	$25.11	$25.10	$25.10
Purchase #6	$100.99	3.566%	$104.5913	$104.59	$104.60	$104.60
Purchase #7	$204.82	9.795%	$224.8821	$224.88	$224.90	$224.90
7 purchase totals =	$803.39		$875.5290	$875.53	$875.55	$875.50