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	$250.82	7.754%	$270.2686	$270.27	$270.25	$270.30
Purchase #2	$206.50	8.198%	$223.4289	$223.43	$223.45	$223.40
Purchase #3	$118.29	6.229%	$125.6583	$125.66	$125.65	$125.70
Purchase #4	$127.32	7.243%	$136.5418	$136.54	$136.55	$136.50
Purchase #5	$6.30	3.737%	$6.5354	$6.54	$6.55	$6.50
Purchase #6	$166.78	4.567%	$174.3968	$174.40	$174.40	$174.40
Purchase #7	$43.33	4.731%	$45.3799	$45.38	$45.40	$45.40
7 purchase totals =	$919.34		$982.2097	$982.22	$982.25	$982.20