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	$143.71	4.630%	$150.3638	$150.36	$150.35	$150.40
Purchase #2	$246.51	3.677%	$255.5742	$255.57	$255.55	$255.60
Purchase #3	$163.69	11.127%	$181.9038	$181.90	$181.90	$181.90
Purchase #4	$40.44	12.154%	$45.3551	$45.36	$45.35	$45.40
Purchase #5	$86.71	3.614%	$89.8437	$89.84	$89.85	$89.80
Purchase #6	$137.27	13.212%	$155.4061	$155.41	$155.40	$155.40
Purchase #7	$38.73	12.183%	$43.4485	$43.45	$43.45	$43.40
7 purchase totals =	$857.06		$921.8952	$921.89	$921.85	$921.90