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	$131.77	3.856%	$136.8511	$136.85	$136.85	$136.90
Purchase #2	$170.39	8.645%	$185.1202	$185.12	$185.10	$185.10
Purchase #3	$95.52	3.760%	$99.1116	$99.11	$99.10	$99.10
Purchase #4	$211.81	4.126%	$220.5493	$220.55	$220.55	$220.50
Purchase #5	$197.73	11.293%	$220.0596	$220.06	$220.05	$220.10
Purchase #6	$41.94	3.311%	$43.3286	$43.33	$43.35	$43.30
Purchase #7	$107.54	3.106%	$110.8802	$110.88	$110.90	$110.90
7 purchase totals =	$956.70		$1,015.9006	$1,015.90	$1,015.90	$1,015.90