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	$189.56	3.856%	$196.8694	$196.87	$196.85	$196.90
Purchase #2	$131.49	12.219%	$147.5568	$147.56	$147.55	$147.60
Purchase #3	$193.81	7.216%	$207.7953	$207.80	$207.80	$207.80
Purchase #4	$36.86	10.505%	$40.7321	$40.73	$40.75	$40.70
Purchase #5	$241.61	8.577%	$262.3329	$262.33	$262.35	$262.30
Purchase #6	$55.96	9.649%	$61.3596	$61.36	$61.35	$61.40
Purchase #7	$38.81	13.105%	$43.8961	$43.90	$43.90	$43.90
7 purchase totals =	$888.10		$960.5422	$960.55	$960.55	$960.60