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	$128.95	6.556%	$137.404	$137.40	$137.40	$137.40
Purchase #2	$141.39	10.718%	$156.5442	$156.54	$156.55	$156.50
Purchase #3	$49.85	5.484%	$52.5838	$52.58	$52.60	$52.60
Purchase #4	$85.30	11.790%	$95.3569	$95.36	$95.35	$95.40
Purchase #5	$250.55	4.424%	$261.6343	$261.63	$261.65	$261.60
Purchase #6	$45.38	12.297%	$50.9604	$50.96	$50.95	$51.00
Purchase #7	$51.27	5.446%	$54.0622	$54.06	$54.05	$54.10
7 purchase totals =	$752.69		$808.5458	$808.53	$808.55	$808.60